The novel liquid-crystalline mixtures (in the case of ferroelectric behavior they additionally contain an optically active compound as dope) are based on at least two mixture components of the general formula (I) and at least one carboxylate of the general formula (II), (III) or (IV). ##STR1## The mixtures have favorable properties for use in electrooptical display elements, such as high contrast, low melting point and short switching times.

Ferroelectric liquid crystals have recently attracted interest as a display 
medium in electrooptical assemblies (for example Lagerwall et al., 
"Ferroelectric Liquid Crystals for Displays", SID Symposium, October 
Meeting 1985, San Diego, Calif. USA). 
For practical use of ferroelectric liquid crystals in electrooptical 
displays, chiral, tilted, smectic phases, such as S.sub.c phases, are 
required (R. B. Meyer, L. Liebert, L. Strzelecki and P. Keller, J. 
Physique 36, L-69 (1975).vertline., which are stable over a broad 
temperature range. This aim can be achieved by means of compounds which 
themselves form such phases, for example S.sub.c phases, or, however, by 
doping compounds which form non-chiral, tilted, smectic phases, with 
optically active compounds (M. Brunet, C. Williams, Ann. Phys. 3, 237 
(1978).vertline.. 
Furthermore, a unitary planar orientation of the liquid crystals is 
necessary in order to achieve a high contrast ratio when ferroelectric 
liquid-crystal mixtures are used in electrooptical assemblies. It has been 
shown that a unitary planar orientation in the S.sub.c phase can be 
achieved if the phase sequence of the liquid-crystal mixture with 
decreasing temperature is as follows: 
Isotropic T nematic T smectic A T smectic C. 
(for example K. Flatischler et al., Mol. Cryst. Liq. Cryst. 131, 21 (1985); 
T. Matsumoto et al., p. 468-470, Proc. of the 6th Int. Display Research 
Conf., Japan Display, 30 Sep. - 2 Oct. 1986, Tokyo, Japan; M. Murakami et 
al., ibid., p. 344-347). 
For ferroelectric (chiral smectic) liquid-crystal mixtures, the condition 
that the pitch of the helix must be large, i.e. greater than 5 .mu.m, in 
the S.sub.c * phase and must be very large, i.e. greater than 10 .mu.m or 
infinite, in the N* phase must additionally be fulfilled. 
The optical switching time .tau.[.mu.s] of ferroelectric liquid-crystal 
systems, which should be as short as possible, depends on the rotation 
viscosity of the system .gamma.[mPas], the spontaneous polarization 
P.sub.s [nC/cm.sup.2 ] and the electric field strength E[V/m], in 
accordance with the equation 
##EQU1## 
Since the field strength E is determined by the electrode separation in 
the electrooptical assembly and by the applied voltage, the ferroelectric 
display medium must have low viscosity and high spontaneous polarization 
in order that a short switching time is achieved. 
Finally, besides thermal, chemical and photochemical stability, a small 
optical anisotropy .DELTA.n, preferably &lt;0.13, and a small positive or, 
preferably, negative dielectric anisotropy .DELTA..epsilon. are required. 
(S. T. Lagerwall et al., "Ferroelectric Liquid Crystals for Displays" SID 
Symposium, Oct. Meeting 1985, San Diego, Calif., USA). 
It is only possible to satisfy all these demands using mixtures comprising 
several components. The basis (or matrix) used here is preferably 
compounds which if possible themselves already have the desired phase 
sequence I.fwdarw.N.fwdarw.S.sub.1 .fwdarw.S.sub.c. Further components of 
the mixture are often added to reduce the melting point and to broaden the 
S.sub.c and usually also the N phase, to induce optical activity, for 
pitch compensation and to match the optical and dielectric anisotropy; 
however, the rotation viscosity, for example, should if possible not be 
increased at the same time. 
It is known that certain derivatives of phenylpyrimidine, in particular 
5-alkyl-2(4-alkoxyphenyl)pyrimidines, are capable of forming S.sub.c, 
S.sub.A and N phases (D. Demus and H. Zaschke, "Flussige Kristalle in 
Tabellen", [Liquid Crystals in Tables], VEB Deutscher Verlag fur 
Grundstoffindustrie, Leipzig 1974, pp. 260-261) and, in addition, can be 
converted into ferroelectric liquid-crystal mixtures by addition of 
optically active dopes [L. M. Blinov et al., Sow. Phys. lisp. 27 (7), 492 
(1984); L. A. Beresnew et al., Ferroelectrics, 59 (321]/1 (1984), 
presented at the 5th Conference of Soc. Countries on Liquid Crystals, 
Odessa, USSR, Oct. 1983; DE-A-3,515,347, EP-A 0,206,228 and EP-A 
0,225,195]. 
It is furthermore known that lower melting points and a broadening of the 
liquid-crystalline phases desired can be achieved by mixing several 
liquid-crystalline compounds [D. Demus et al., Mol. Cryst. Liq. Cryst. 25, 
215 (1974), J. W. Goodby, Ferroelectrics 49, 275 (1983)], and that the 
melting-point depression is the more pronounced the more the mixture 
components also differ structurally. (J. S. Dave et al., J. Chem. Soc. 
1955, 4305). It was thus to be presumed that particularly low mixture 
melting points, and thus low phase-transition points of the S.sub.c phase, 
are obtained when compounds are mixed which, on the one hand, are 
significantly different structurally, but, on the other hand, are 
sufficiently similar to be readily miscible. 
DE-C 2,257,588 discloses a 5-butoxy-2(4-pentoxyphenyl)-pyrimidine, but this 
only forms a nematic phase. 
In DE 3,831,226.3, it has been found that, as the base component, compounds 
of the type 5-alkoxy-2(4-alkoxyphenyl)pyrimidines of the general formula 
(I) 
##STR2## 
in which C.sub.n H.sub.2n+1 and C.sub.x H.sub.2x+1 are straight-chain 
alkyl radicals in which n is an integer from 6 to 14 and x is an integer f 
rom 2 to 14, are particularly highly suitable [lacuna] the matrix (base) 
for liquid-crystalline mixtures, in particular ferroelectric 
liquid-crystalline mixtures; of them, at least two different compounds a' 
and a" are present in the mixture. For the most part, they exhibit the 
desired phase sequence ITNTS.sub.A TS.sub.c with decreasing temperature. 
Compared with the known 5-alkyl-2-(4-alkoxyphenyl)pyrimidines, they have 
considerably broader S.sub.c phases and higher transition temperatures of 
the S.sub.c TS.sub.A transition. In addition, the S.sub.c phase is even 
formed in the case of a lower number of carbon atoms in the alkyl(oxy) 
chains, for example even when n =8 and x 2 or n =6 and x 6. Compared with 
the known 5-alkyl-2-(4-alkoxyphenyl)pyrimidines, this gives a greater 
choice of homologous, readily miscible compounds having S.sub.c phases for 
preparing the mixture. Due to their higher phase-transition temperatures 
S.sub.A to S.sub.c (for example 70.degree. to 90.degree. C.) and their 
broader S.sub.c phases, they also make it possible to prepare mixtures 
having very broad S.sub.c phases (for example up to about 68.degree. C.) 
and high transition temperatures S.sub.A /S.sub.c. 
The mixtures of DE 3,831,226.3 of compounds of the formula (I) are already 
very highly suitable as a matrix for ferroelectric liquid-crystalline 
mixtures. However, they also have a large optical anisotropy (.DELTA.n) 
and a large positive dielectric anisotropy (.DELTA..epsilon.). In 
addition, the nematic phase, depending on the chain length n or x of the 
substituents, is still narrow. 
By adding at least one compound (cyclohexanecarboxylate) of the general 
formula (II), i.e. a compound of type b, 
##STR3## 
the parameters [.DELTA.n] and [.DELTA..epsilon.] can simultaneously be 
optimized and the width of the nematic phase can be matched to practical 
requirements. 
In the general formula (II): 
R.sup.1 is an alkyl chain having 10 to 16 carbon atoms or an alkoxy chain 
having 8 to 14 carbon atoms, and R.sup.2 is an alkyl chain having 2 to 9 
carbon atoms. These compounds are described in DE-A 3,731,639. They 
develop their favorable action even when added in amounts from about 2 mol 
%, relative to the mixture of the components of type a and b. When added 
in amounts from about 10 and up to about 40 mol %, the nematic phase is 
broadened by about 8 to 18.degree. C. and the smectic phase by about 
6.degree. to 15.degree. C. In addition, it is very advantageous that the 
addition only insignificantly increases the rotation viscosity of the base 
mixture according to the invention, which is already very low per se. 
The melting point and the lower phase-transition temperature of the S.sub.c 
phase of the mixtures can be reduced, if they are too high, by adding at 
least one compound (alkenyloxyphenylpyrimidine derivative) of the general 
formula (III), i.e. a compound of type c, to mixtures of compounds of type 
a alone or additionally containing compounds of type b: 
##STR4## 
In the general formula (III), R.sup.3 is a branched or straight-chain alkyl 
radical having 7 to 16 carbon atoms or a straight-chain or branched alkoxy 
radical having 6 to 14 carbon atoms, and y is an integer f rom 4 to 14. 
These compounds are described in DE-A 3,731,638. Added amounts of from 
about 10 to 35 mol %, relative to the overall mixture, reduce the lower 
temperature limit of the S.sub.c phase by up to 5.degree. C. The other 
favorable physical properties of the mixtures are generally not impaired 
by this addition. 
To reduce the melting point and the lower temperature limit of the S.sub.c 
phase, it is also possible to add, together with or in place of compounds 
of type c, other compounds of the formula (IV), i.e. of type d, 
##STR5## 
where m and p, independently of one another, are integers from 6 to 14. 
When amounts of from about 10 to 25 mol % of the compound of type d or 
mixtures with compounds of type c, relative to the overall mixture, are 
added to mixtures of compounds of type a or a and b, the lower temperature 
limit of the S.sub.c phase is reduced by up to 10.degree. C. 
Some of these components, and also certain mixtures, are already known from 
the prior art. However, since the development, in particular of 
ferroelectric liquid-crystal mixtures, can in no way be regarded as 
complete, the manufacturers of display elements are interested in a very 
wide variety of mixtures. A further reason for this, amongst others, is 
that conclusions on the quality of the liquid-crystalline mixtures too can 
only be made by considering the interactions of the liquid-crystalline 
mixtures with the individual assemblies of the display elements or of the 
cells (for example the orientation layer). 
The object of the present invention is therefore to provide compositions of 
suitable components for liquid-crystalline base mixtures, but also for 
ferroelectric liquid-crystalline mixtures, which satisfy as many as 
possible of the abovementioned criteria, have, in particular, a low 
melting point and furthermore result in improved contrast in a display. 
The invention relates to the liquid-crystalline base mixtures characterized 
below, which contain, on the one hand, compounds A from DE 3,831,226.3, 
but, on the other hand, also contain at least one carboxylate C of the 
general formula (V), (VI), (VII), (VIII) or (IX) as a mixture component. 
The invention furthermore relates to liquid-crystalline mixtures having 
favorable values for the optical anisotropy and the dielectric anisotropy 
and having a broad nematic phase which is sufficient for practical use. 
A preferred subject-matter of the invention are likewise ferroelectric 
liquid-crystalline mixtures having a short switching time, the phase 
sequence I.fwdarw.N*.fwdarw.S.sub.A, S.sub.c *, the pitch in the nematic 
phase being &gt;15 .mu.m and in the S.sub.c * phase being &gt;5 .mu.m, and 
having a negative .DELTA..epsilon. and .DELTA.n&lt;0.15, and which contain a 
chiral dope C in addition to the components A and the carboxylates B. 
The novel invention relates to liquid-crystalline mixtures containing, as 
component A, at least two 5-alkoxy-2-(alkoxyphenyl)pyrimidines of the 
general formula (I) 
##STR6## 
in which the alkyl radicals are straight-chain alkyl radicals in which n 
is an integer from 6 to 14 and x is an integer from 2 to 14, and, if 
appropriate, one or more cyclohexanecarboxylates of the general formula 
(II) 
##STR7## 
in which R.sup.1 is an alkyl radical having 10 to 16 carbon atoms or an 
alkoxy radical having 8 to 14 carbon atoms, and R.sup.2 is an alkyl 
radical having 2 to 9 carbon atoms, and, if appropriate, one or more 
alkenyloxyphenylpyrimidine derivatives of the general formula (III) 
##STR8## 
in which R.sup.3 is an alkyl chain having 7 to 16 carbon atoms or an 
alkoxy chain having 6 to 14 carbon atoms, and y is an integer from 4 to 
14, and, if appropriate, one or more alkylpyrimidinealkoxyphenyl 
derivatives of the general formula (IV) 
##STR9## 
in which m and p, independently of one another, are integers from 6 to 14, 
and if appropriate as component B (for ferroelectric liquid-crystal 
mixtures), at least one optically active compound from the group 
a) optically active esters made from .alpha.-chlorocarboxylic acids and 
mesogenic phenols, 
b) optically active esters of N-acylproline, 
c) optically active esters of 1,3-dioxolane-4-carboxylic acids, and 
d) optically active esters of oxirane-2-carboxylic acids, 
wherein the liquid-crystal mixtures furthermore contain at least one 
carboxylate of the general formula (V), (VI), (VII), (VIII) or (IX) as a 
mixture component: 
##STR10## 
where k may be an integer from 6 to 14, and 
l may be an integer from 2 to 14, 
##STR11## 
where m may be an integer from 5 to 14, and 
l may be an integer from 2 to 14, 
##STR12## 
where p may be an integer from 7 to 14, and 
r may be an integer from 4 to 14, 
##STR13## 
where s may be an integer from 6 to 14, and 
t may e an integer from 6 to 14, 
##STR14## 
where R.sup.2 is straight-chain or branched (C.sub.1 -C.sub.12)alkyl or 
alkenyl, it being possible for one or two non-adjacent CH.sub.2 groups to 
be replaced by O and/or S atoms, 
Y is F, Cl, Br, CN or CF.sub.3 and 
R.sup.1 is branched (C.sub.3 -C.sub.9)alkyl, benzyl or phenyl. 
Preferred liquid-crystal mixtures are those which contain, as component C, 
at least one 4-(5-alkylpyrimidin-2-yl)phenyl carboxylate of the general 
formula (V) 
##STR15## 
where k may be an integer from 6 to 14, and 
l may be an integer from 4 to 14. 
Likewise preferred mixtures are those which contain, as component C, at 
least one 4-(5-alkoxypyrimidin-2-yl)-phenyl carboxylate of the general 
structure (VI) 
##STR16## 
where m may be an integer from 6 to 14, and 
l may be an integer from 4 to 14. 
Preferred liquid-crystalline mixtures are also those which contain, as 
component C, at least one benzoate of the general structure (VII) 
##STR17## 
where p may be an integer from 7 to 14, and 
r may be an integer from 4 to 14. 
Likewise preferred mixtures are those which contain, as component C, at 
least one benzoate of the general structure (VIII) 
##STR18## 
where s may be an integer from 6 to 14, and 
t may be an integer from 6 to 14. 
In addition, preferred mixtures are those which contain, at least as one 
component, a racemate of the structure (IX) 
##STR19## 
where R.sup.2 is straight-chain or branched (C.sub.1 -C.sub.12)alkyl or 
alkenyl, it being possible for one or two non-adjacent CH.sub.2 groups to 
be replaced by O and/or S atoms, 
Y is F, Cl or CF.sub.3 and 
R.sup.1 is branched (C.sub.3 -C.sub.9)alkyl, benzyl or phenyl. 
Particularly preferred liquid-crystal mixtures are those which contain, as 
component C, the racemate of at least one .alpha.-halocarboxylate of the 
structure (IXa) 
##STR20## 
where R.sup.2 may be an alkyl radical or an alkenyl radical having 1 to 12 
carbon atoms whose CH.sub.2 group bonded to the aromatic rings may also be 
replaced by O and/or [lacuna], and y is F or Cl. 
Very particularly suitable here are the .alpha.-halocarboxylic acids of the 
structures (IXb) and (IXc) 
##STR21## 
It has now been found that the FLC mixtures according to the invention 
which contain, as component C, 2 to 25 mol-%, in particular 10 to 25 
mol-%, of mixtures of individual compounds of the general structures (V) 
and/or (VI) and/or (VIII) and/or (VIII) and/or (IX) have an upper 
phase-transition point which is up to 10.degree. C. lower than the 
corresponding mixtures without the components according to the invention. 
Furthermore, the contrast is increased by up to 10% and, in some cases, the 
switching times are also reduced by the addition. 
Through the specific addition of the abovementioned compounds of the 
formulae (V to IX), the physical parameters [.DELTA.n] and 
[.DELTA..epsilon.] of the mixture can be optimized, i.e. matched to the 
particular specific requirements of the display element. 
Surprisingly, it has furthermore been observed that liquid-crystalline 
mixtures which contain 2 to 15 mol-% of racemic mixtures of one or more 
esters of the general structure (IX) have a melting point which is lower 
by up to 5.degree. C. and an upper S.sub.c phase transition point which is 
lower by up to 10.degree. C. than the corresponding base mixture without 
this (these) component(s). The contrast of the mixtures according to the 
invention is up to 20% higher than that of the base mixtures. Doping with 
a racemic mixture of the .alpha.-chlorocarboxylate (IXb) 
##STR22## 
has proven particularly suitable here. 
The liquid-crystal mixtures according to the invention are suitable both as 
base mixtures and, when chiral dopes B are added, as novel ferroelectric 
liquid-crystal mixtures which are particularly suitable for practical use 
in electrooptical switching and display elements. 
As already proposed (DE 3,831,226.3), the following dopes have proven 
particularly suitable for the purpose of the invention: 
a) optically active esters made from .alpha.-chlorocarboxylic acids and 
mesogenic phenols as in DE-A 3,703,228, and, in particular, the optically 
active ester of the formula below 
##STR23## 
where r=4 to 8 b) optically active esters of N-acylproline as in DE-A 
3,644,522 
c) optically active esters of 1,3-dioxolane-4-carboxylic acids as in DE-A 
3,713,273 
d) optically active esters of oxirane-2-carboxylic acids as in DE-A 
3,718,174. 
These dopes frequently induce ferroelectric behavior even when added in 
small amounts from 0.5 and in particular from 3 mol-%, relative to the 
overall mixture. The upper limit for the amount added is 30 mol-%. 
The addition of these dopes generally further reduces the melting point and 
the lower temperature limit of the S.sub.c * phase. In addition, depending 
on the nature and amount of the dope, the upper temperature limit of the 
S.sub.c * phase may be reduced or increased and the width of the N* phase 
may be changed, which should be taken into account when preparing the 
matrix mixture. As is known, the optically active dope induces helical 
twisting in the S.sub.c phase and in the N phase, which converts these 
phases into the S.sub.c * phase and N* phase respectively. The pitch and 
the rotation sense of these helices in the N* phase depend on the nature 
and amount of the optically active dope. They must frequently be 
compensated by adding a further dope which induces a helix with the 
opposed rotation sense. In general, a ferroelectric liquid-crystal mixture 
should have a helix with a pitch of greater than 10 .mu.m in the N* phase 
and of at least 5 .mu.m in the S.sub.c * phase. The compounds used for 
compensation of the pitch should preferably not induce in the mixture any 
spontaneous polarization or should only do so to a negligibly small 
extent, or should induce a spontaneous polarization with the same sign as 
the optically active dope. 
If pitch compensation is necessary, the following combinations are 
particularly suitable in the mixtures according to the invention: 
a.sub.1) Optically active .alpha.-chlorocarboxylates induce a negative 
P.sub.s and a helix with negative rotation sense. For compensation, 
derivatives of citronellol of the general formula (N) are advantageously 
added 
##STR24## 
In this formula, q is an integer from 6 to 16, A is an oxygen atom or a 
chemical bond, and B is a pyrimidine-2,5-diyl ring, it being possible for 
the phenylene ring bonded thereto to be in the 2- or 5-position. For pitch 
compensation, up to 4 mol %, relative to the overall mixture, or one mole 
of citronellol derivative are required per 7 to 13 moles of 
.alpha.-chlorocarboxylate. 
b.sub.1) Optically active N-acylproline esters having the S configuration 
at the asymmetric carbon atom which induce a positive P.sub.s and a 
negative pitch in the mixtures according to the invention can be 
compensated by adding optically active oxirane-2-carboxylates as in DE-A 
3,718,174 having a positive P.sub.s and, in particular, a 2-R-3-R 
configuration. The amount to be added is up to 6 mol %, relative to the 
overall mixture or 1 mole of oxirane-2-carboxylate per 5 to 9 moles of 
N-acylproline ester. 
c.sub.1) The compensation in the case of optically active 
1,3-dioxolane-4-carboxylates having the R configuration, which likewise 
induce a positive P.sub.s and a negative pitch, is likewise expediently 
carried out as described under b,) using oxirane-2-carboxylates. 
The use of oxirane-2-carboxylates as described in b.sub.1) and c.sub.1) has 
the additional advantage that these compounds themselves induce a very 
high positive P.sub.s and thus increase the P.sub.s of the overall mixture 
and shorten the switching time. 
The values of spontaneous polarization P.sub.s [nC /CM.sup.2 ], the 
contrast K, the optical switching time .tau. [.mu.s], the dielectric 
anisotropy .DELTA..epsilon. and the optical anisotropy .DELTA.n were 
determined for the ready-to-use ferroelectric liquid-crystal mixtures (all 
measurements at 25.degree. C.). 
The P.sub.s values are measured by the method of H. Diamant et al. (Rev. 
Sci. Instr., 28, 30, 1957), where measurement cells with an electrode 
separation of 2 .mu.m and ground polyamide as the orientation layer are 
used. 
To determine .tau. and K, the measurement cell is clamped between crossed 
analyzer and polarizer on the rotary stage of a polarizing microscope. 
To determine the contrast (K), the measurement cell is positioned, by 
rotation, so that a photodiode indicates minimum light transmission (dark 
state). The microscope illumination is adjusted so that the photodiode 
indicates the same light intensity for all cells. After a switching 
operation, the light intensity changes (bright state), and the contrast is 
calculated from the ratio of the light intensities in these states. 
The switching time .tau. is determined using a photodiode by measuring the 
time taken for the light signal to increase from a signal height of 10 to 
90 %. The switching voltage comprises rectangular pulses and is +10 
V/.mu.m. 
The phase-transition temperatures are determined using a polarizing 
microscope from the texture changes on heating. By contrast, the melting 
point is determined using a DSC instrument. The phase-transition 
temperatures between the phases 
______________________________________ 
Nematic (N or N*) 
Smectic-C (S.sub.c or S.sub.c *) 
Smectic-A (S.sub.A or S.sub.A *) 
Crystalline (X) 
______________________________________ 
are given in .degree.C., and the values are between the phase symbols in 
the phase sequence.

Example 1 
a) a liquid-crystalline mixture comprising the following eight components 
______________________________________ 
5-octoxy-2-(4-hexoxyphenyl)pyrimidine 
14 mol-% 
5-octoxy-2-(4-octoxyphenyl)pyrimidine 
5 mol-% 
5-octoxy-2-(4-butoxyphenyl)pyrimidine 
15 mol-% 
5-octoxy-2-(4-decoxyphenyl)pyrimidine 
8 mol-% 
5-octoxy-2-(4-dodecoxyphenyl)pyrimidine 
8 mol-% 
5-octyl-2-(4-decoxyphenyl)pyrimidine 
13 mol-% 
[4-(5-decylpyrimidin-2-yl)]phenyl trans- 
17 mol-% 
4-pentylcyclohexanecarboxylate 
##STR25## 
[4-(5'-octylpyrimidin-2-yl)]phenyl 
20 mol-% 
heptanoate (= compound of the general formula V) 
exhibits the following liquid-crystalline phase 
ranges: 
X -5 S.sub.c 71 S.sub.A 78 N 93 I 
______________________________________ 
b) The following mixture, which is claimed in DE 3,831,226.3 and differs 
from the mixture 1a only in that it contains no component of the general 
formula V, is suitable for comparing the physical properties. This mixture 
comprising seven components has the following liquid-crystalline phase 
ranges: 
______________________________________ 
X -1 S.sub.c 81 
S.sub.A 87 
N 103 I 
______________________________________ 
Compared with the mixture 1b, the mixture 1a according to the invention has 
a melting point (X) which is lower by 4.degree. C. and an upper S.sub.c 
phase-range limiting temperature which is lower by 10.degree. C. 
Example 2 
a) A liquid-crystalline mixture comprising the following eight components 
______________________________________ 
5-octoxy-2-(4-hexoxyphenyl)pyrimidine 
16 mol-% 
5-octoxy-2-(4-octoxyphenyl)pyrimidine 
6 mol-% 
5-octoxy-2-(4-butoxyphenyl)pyrimidine 
15 mol-% 
5-octoxy-2-(4-decoxyphenyl)pyrimidine 
8 mol-% 
5-octoxy-2-(4-dodecoxyphenyl)pyrimidine 
8 mol-% 
5-octyl-2-(4-dodecoxyphenyl)pyrimidine 
13 mol-% 
[4-(5-decylpyrimidin-2-yl)]phenyl trans- 
19 mol-% 
4-pentylcyclohexanecarboxylate 
##STR26## 
[4-(5'-octylpyrimidin-2-yl)]phenyl 
15 mol-% 
heptanoate (= compound of the general formula V) 
exhibits the following liquid-crystalline phase 
ranges: 
X -5 S.sub.c 75 S.sub.A 80 N 87 I 
______________________________________ 
b) The following mixture, which is claimed in DE 3,831,226.3 and differs 
from the mixture 2a only in that it contains no component of the general 
formula V, is suitable for comparing the physical properties. 
This mixture comprising seven components has the following 
liquid-crystalline phase ranges: 
______________________________________ 
X -2 S.sub.c 81 
S.sub.A 86 
N 104 I 
______________________________________ 
Compared with the mixture 2b, the mixture 2a according to the invention has 
a melting point which is lower by 3.degree. C. and an upper S.sub.c 
phase-range limiting temperature which is lower by 6.degree. C. 
Example 3 
a) A liquid-crystalline mixture comprising the following eight components 
______________________________________ 
5-octoxy-2-(4-decoxyphenyl)pyrimidine 
15 mol-% 
5-octoxy-2-(4-octoxyphenyl)pyrimidine 
6 mol-% 
5-octoxy-2-(4-butoxyphenyl)pyrimidine 
15 mol-% 
5-octoxy-2-(4-decoxyphenyl)pyrimidine 
8 mol-% 
5-octoxy-2-(4-dodecoxyphenyl)pyrimidine 
8 mol-% 
5-octyl-2-(4-dodecoxyphenyl)pyrimidine 
14 mol-% 
[4-(5-decylpyrimidin-2-yl)]phenyl trans- 
14 mol-% 
4-pentylcyclohexanecarboxylate 
##STR27## 
[4-(5-octylpyrimidin-2-yl)]phenyl 
20 mol-% 
heptanoate (= compound of the general formula V) 
exhibits the following liquid-crystalline phase 
ranges: 
X -3.5 S.sub.C 69 S.sub.A 80 N 92 I 
______________________________________ 
b) The following mixture, which is claimed in DE 3,831,226.3 and differs 
from the mixture 3a only in that it contains no component of the general 
formula V, is suitable for comparing the physical properties. 
This mixture comprising seven components has the following 
liquid-crystalline phase ranges: 
______________________________________ 
X 0 S.sub.c 80 
S.sub.A 88 
N 102 I 
______________________________________ 
In comparison, the mixture 3a according to the invention has a melting 
point which is 3.5.degree. C. lower and an upper S.sub.c phase-range 
limiting temperature which is 11.degree. C. lower. 
Example 4 
a) A liquid-crystalline mixture comprising the following eight components 
______________________________________ 
5-octoxy-2-(4-hexoxyphenyl)pyrimidine 
16 mol-% 
5-octoxy-2-(4-octoxyphenyl)pyrimidine 
6 mol-% 
5-octoxy-2-(4-butoxyphenyl)pyrimidine 
16 mol-% 
5-octoxy-2-(4-decoxyphenyl)pyrimidine 
8 mol-% 
5-octoxy-2-(4-dodecoxyphenyl)pyrimidine 
8 mol-% 
5-octyl-2-(4-dodecoxyphenyl)pyrimidine 
14 mol-% 
[4-(5-decylpyrimidin-2-yl)]phenyl trans- 
22 mol-% 
4-pentylcyclohexanecarboxylate 
##STR28## 
4-(5-decylpyrimidin-2-yl)phenyl 
10 mol-% 
dodecanoate (= compound of the general formula V) 
exhibits the following liquid-crystalline phase 
ranges: 
X -5.5 S.sub.c 79 S.sub.A 84 N 94 I 
______________________________________ 
b) The following mixture, which is claimed in DE 3,831,226.3 and differs 
from the mixture 4a only in that it contains no component of the general 
formula V, is suitable for comparing the physical properties. 
This mixture comprising seven components has the following 
liquid-crystalline phase ranges: 
______________________________________ 
X -2 S.sub.c 81 
S.sub.A 86 
N 104 I 
______________________________________ 
In comparison, the mixture 4a according to the invention has a melting 
point which is 3.5.degree. C. lower and an upper S.sub.c phase-range 
limiting temperature which is 2.degree. C. lower. 
Example 5 
a) A liquid-crystalline mixture comprising the following nine components 
______________________________________ 
5-octoxy-2-(4-decoxyphenyl)pyrimidine 
7.5 mol-% 
5-octoxy-2-(4-octoxyphenyl)pyrimidine 
4 mol-% 
5-octoxy-2-(4-hexoxyphenyl)pyrimidine 
9 mol-% 
5-octoxy-2-(4-butoxyphenyl)pyrimidine 
9.5 mol-% 
5-octyl-2-(4-decoxyphenyl)pyrimidine 
9.5 mol-% 
5-octyl-2-(4-hexoxyphenyl)pyrimidine 
14 mol-% 
5-octyl-2-(4-octoxyphenyl)pyrimidine 
13 mol-% 
[4-(5-decylpyrimidin-2-yl)]phenyl trans- 
28.5 mol-% 
4-pentylcyclohexanecarboxylate 
##STR29## 
4-(5-octylpyrimidin-2-yl)phenyl 
5 mol-% 
decanoate (= compound of the general formula V) 
exhibits the following liquid-crystalline phase 
ranges: 
X -3 S.sub.c 68 N 94 I 
______________________________________ 
b) A comparable mixture which differs from the mixture 5a only in that it 
contains no component of the general formula V has the following 
liquid-crystalline phase ranges: 
______________________________________ 
X -2 S.sub.c 80 N 99 I 
The addition of the component of the general 
formula V has thus resulted in a reduction of the 
melting point by 1.degree. C. 
______________________________________ 
Example 6 
a) A liquid-crystalline mixture comprising the following eight components 
______________________________________ 
5-octoxy-2-(4-hexoxyphenyl)pyrimidine 
16 mol-% 
5-octoxy-2-(4-octoxyphenyl)pyrimidine 
6 mol-% 
5-octoxy-2-(4-butoxyphenyl)pyrimidine 
15 mol-% 
5-octoxy-2-(4-decoxyphenyl)pyrimidine 
8 mol-% 
5-octoxy-2-(4-dodecoxyphenyl)pyrimidine 
8 mol-% 
5-octyl-2-(4-dodecoxyphenyl)pyrimidine 
13 mol-% 
[4-(5-decylpyrimidin-2-yl)]phenyl trans- 
19 mol-% 
4-pentylcyclohexanecarboxylate 
##STR30## 
4-(5-octylpyrimidin-2-yl)phenyl 
15 mol-% 
undecanoate (= compound of the general formula V) 
exhibits the following liquid-crystalline phase 
ranges: 
X -5 S.sub.c 75 S.sub.A 80 N 87 I 
______________________________________ 
b) The following mixture, which is claimed in DE 3,831,226.3 and differs 
from the mixture 6a only in that it contains no component of the general 
formula V, is suitable for comparing the physical properties. 
This mixture comprising seven components has the following 
liquid-crystalline phase ranges: 
______________________________________ 
X -2 S.sub.c 81 
S.sub.A 86 
N 104 I 
______________________________________ 
In comparison, the mixture 6a according to the invention has a melting 
point which is 3.degree. C. lower and an upper S.sub.c phase-range 
limiting temperature which is 6.degree. C. lower. 
Example 7 
The following ferroelectric mixtures comprising the following components 
##STR31## 
In Table 1 below, the property features of the examples are reproduced in a 
summarized form. 
TABLE 1 
__________________________________________________________________________ 
Concentration Switching time 
Polarization 
Phase-transition temperatures 
X Y Contrast 
.tau. P.sub.s 
X.fwdarw.S.sub.c * 
S.sub.c *.fwdarw.S.sub.A * 
S.sub.A *.fwdarw.N* 
N*.fwdarw.I 
Example 
Mol % 
Mol % 
K .mu.s nC .multidot. cm.sup.-2 
.degree.C. 
.degree.C. 
.degree.C. 
.degree.C. 
__________________________________________________________________________ 
7a 94 0 6.4 75 -10 -1 80 85 99 
7b 79 15 4.6 65 -10.5 -8 73 79 92 
__________________________________________________________________________ 
The results in columns 5 and 7 show very clearly the improvement in the 
switching time by 10 .mu.s and in the melting point by 7.degree. C. with 
increased concentration of the compound of the general formula V. 
Example 8 
a) A ferroelectric mixture comprising the following components 
__________________________________________________________________________ 
mixture from Example 2a 94 mol-% 
##STR32## 6 mol-% 
4-[2-((S)-7-methylnonoxy)pyrimidin-5-yl]phenyl (2S,3S)-2-chloro-3-methylpe 
ntanoate 
exhibits the following LC ranges 
X -9 S.sub.c * 72 S.sub.A * 78 N* 93 I 
__________________________________________________________________________ 
At 25.degree. C., this mixture has a polarization of -9 nC.cm.sup.-2 and, 
in a switching field of 10 V.mu.m.sup.-1, a switching time of 55 .mu.s. 
For comparison, a mixture based on the base mixture of Example 2b is 
suitable. 
b) The ferroelectric mixture comprising 
__________________________________________________________________________ 
mixture from Example 2b 94 mol-% 
##STR33## 6 mol-% 
4-[2-((S)-7-methylnonoxy)pyrimidin-5-yl]phenyl (2S,3S)-2-chloro-3-methylpe 
ntanoate 
exhibits the following liquid-crystalline phase ranges: 
X -7 S.sub.c 79 S.sub.A 84 N 99 I 
__________________________________________________________________________ 
At 25.degree. C., this mixture has a spontaneous polarization of -9 nC 
cm.sup.-2, a contrast of 5.6 and, in a switching field of 10 
V.mu.m.sup.-1, a switching time of 60 .mu.s. 
Compared with the mixture 9a, this mixture contains no component of the 
general formula VI and, in comparison, has a melting point which is 
2.degree. C. higher and a switching time which is 5 .mu.s longer. 
Example 9 
A ferroelectric mixture comprising the following four components 
__________________________________________________________________________ 
mixture from Example 2b 64 mol-% 
##STR34## 15 mol-% 
4-(decylpyrimidin-2-yl)phenyl nonanoate (compound of the general formula 
V) 
##STR35## 15 mol-% 
4-(5-decylpyrimidin-2-yl)phenyl undecanoate (compound of the general 
formula V) 
##STR36## 6 mol-% 
4-[2-(S)-7-methylnonoxypyrimidin-5-yl] phenyl(2S,3S)-2-chloro-3-methylpent 
anoate 
exhibits the following liquid-crystalline phase ranges: 
X -11 S.sub. c * 75 S.sub.A * 90 N* 85 I 
__________________________________________________________________________ 
At 25.degree. C., this mixture has a polarization of -8.7 nC cm.sup.-2 a 
contrast of 6.6 [lacuna] in a switching field of 10 V.mu.m.sup.-1, a 
switching time of 50 .mu.s. 
Compared with the mixture 8b, which differs from the mixture 9 only in that 
it contains no compound of the general formula V, the mixture 9 has a 
contrast which is higher by 18%, a melting point which is lower by 
4.degree. C. and a switching time which is shorter by 10 .mu.s. 
Example 10 
A ferroelectric mixture comprising the following components 
__________________________________________________________________________ 
mixture from Example 2a 89 mol-% 
##STR37## 5 mol-% 
4-(2-nonoxypyrimidin-5-yl)phenyl 
2-chloro-4-methyl-pentanoate (racemate) 
(compound of the general formula IX) 
##STR38## 6 mol-% 
4-(2-nonoxypyrimidin-5-yl)phenyl 
(2S,3S)-2-chloro-3-methylpentanoate 
has the phase sequence 
X -9 S.sub.c * 72 S.sub.A * 77 N* 88 I 
__________________________________________________________________________ 
At 25.degree. C., this mixture has a polarization of -8.7 nC cm.sup.-2, a 
contrast of 8 and, in a switching field of 10 V.mu.m.sup.-1, a switching 
time of 60 .mu.s. 
Compared with the ferroelectric mixture of Example 7b, the contrast is 45% 
higher. The addition of the racemic .alpha.-chlorocarboxylate thus results 
in an increase in the contrast and a reduction in the melting point by 
1.degree. C. 
Example 11 
a) A ferroelectric mixture comprising the following components 
__________________________________________________________________________ 
mixture from Example 3a 88 mol-% 
##STR39## 12 mol-% 
4-(2-nonoxypyrimidin-5-yl)phenyl 
(2S,3S)-2-chloro-3-methylpentanoate 
has the phase sequence 
X -7 S.sub.c * 68 S.sub.A * 74 N* 85 I 
__________________________________________________________________________ 
At 25.degree. C., this mixture has a polarization of -20n C cm.sup.-2 
[sic], a contrast of 8.2 and, in a switching field of 10V.mu.m.sup.-1, a 
switching time of 18 .mu.s. 
b) A ferroelectric mixture comprising 
__________________________________________________________________________ 
mixture from Example 3a 85 mol-% 
##STR40## 12 mol-% 
4-(2-nonoxypyrimidin-5-yl)phenyl 
(2S,3S)-2-chloro-3-methylpentanoate 
##STR41## 3 mol-% 
4-(2-nonoxypyrimidin-5-yl)phenyl 2-chloro-4-methyl- 
pentanoate (racemate) 
__________________________________________________________________________ 
has the phase sequence 
______________________________________ 
X -8 S.sub.c * 68 
S.sub.A * 75 
N* 85.5 I 
______________________________________ 
At 25.degree. C., this mixture has a polarization of -20 nC cm.sup.-2, a 
contrast of 8.9 and, in a switching field of 10 V.mu.m.sup.-1, a switching 
time of 17 .mu.s. Compared with the ferroelectric mixture in Example 11a, 
the contrast is higher. The addition of the racemic 
.alpha.-chlorocarboxylate thus results in an increase in the contrast by 
9%. 
Examples 12a-c 
The following ferroelectric mixtures comprising the following components 
##STR42## 
In Table 2 below, the property features (at 25.degree. C.) of the examples 
have been summarized. 
TABLE 2 
__________________________________________________________________________ 
Concentration Switching time 
Polarization 
Phase-transition temperatures 
X Y Contrast 
.tau. P.sub.s 
X.fwdarw.S.sub.c * 
S.sub.c *.fwdarw.S.sub.A * 
S.sub.A *.fwdarw.N* 
N*.fwdarw.I 
Example 
Mol % 
Mol % 
K .mu.s nC .multidot. cm.sup.-2 
.degree.C. 
.degree.C. 
.degree.C. 
.degree.C. 
__________________________________________________________________________ 
12a 94 0 4.5 43 -9.8 -6 70 77 86 
12b 91 3 4.6 44 -9.6 -5.3 
69 77 85 
12c 88 6 5.8 45 -9.2 -5.5 
68 76 84 
__________________________________________________________________________ 
The results in columns 3 and 4 show very clearly the improvement in the 
contrast with the increase in the concentration of the racemic mixture of 
the chlorocarboxylate (Y). 
Examples 13a-c 
The following ferroelectric mixtures comprise the following components 
##STR43## 
In Table 3 below, the property features (at 25.degree. C.) of the examples 
are reproduced in a summarized form. 
TABLE 3 
__________________________________________________________________________ 
Concentration Switching time 
Polarization 
Phase-transition temperatures 
X Y Contrast 
.tau. P.sub.s 
X.fwdarw.S.sub.c * 
S.sub.c *.fwdarw.S.sub.A * 
S.sub.A *.fwdarw.N* 
N*.fwdarw.I 
Example 
Mol % 
Mol % 
K .mu.s nC .multidot. cm.sup.-2 
.degree.C. 
.degree.C. 
.degree.C. 
.degree.C. 
__________________________________________________________________________ 
13a 94 0 4.5 43 -9.8 -6 71 78 89 
13b 91 3 4.7 52 -9.5 -6 71 77 88 
13c 88 6 6.2 53 -9.2 -6 70 77 86 
__________________________________________________________________________ 
The results in columns 3 and 4 show very clearly the improvement in the 
contrast with the increase in the concentration of the racemic mixture of 
the chlorocarboxylate (Y). 
Example 14 
a) A liquid-crystalline mixture comprising the following five components 
______________________________________ 
5-octoxy-2-(4-decoxyphenyl)pyrimidine 
21 mol-% 
5-octoxy-2-(4-octoxyphenyl)pyrimidine 
12 mol-% 
5-octoxy-2-(4-hexoxyphenyl)pyrimidine 
25 mol-% 
5-octoxy-2-(4-butoxyphenyl)pyrimidine 
27 mol-% 
##STR44## 15 mol-% 
4'-hexoxyphenyl 4-octoxybenzoate 
(= compound of the general formula VII) 
has the following liquid-crystalline phase ranges: 
X 8 S.sub.c 72.3 S.sub.A 86.1 N 93 I 
______________________________________ 
b) A mixture without addition of 15 mol-% of the compound of the general 
formula (VII) has, by contrast, the following liquid-crystalline phase 
ranges: 
______________________________________ 
X 13 S.sub.c 81.5 
S.sub.A 95.5 
N 98 I 
______________________________________ 
Compared with mixture 14b, the mixture 14a according to the invention 
additionally contains a component of the general formula (VII) and has, in 
comparison, a melting point which is lower by 5.degree. C. and an upper 
S.sub.c phase-range limiting temperature which is lower by 9.5.degree. C. 
Example 15 
A liquid-crystalline mixture comprising the following five components 
______________________________________ 
mixture from Example 14b 80 mol-% 
##STR45## 20 mol-% 
4-hexoxyphenyl 4'-decoxybenzoate 
(compound of the general formula VII) 
has the following liquid-crystalline phase ranges: 
X 9 S.sub.c 72.6 S.sub.A 87.3 N 92.5 I 
______________________________________ 
Compared with the mixture 14b, the mixture additionally contains a 
component of the general formula (VII) and has, in comparison, a melting 
point which is lower by 4.degree. C. and an S.sub.c phase-range limiting 
temperature which is lower by 9.degree. C. 
Example 16 
A liquid-crystalline mixture comprising the following six components 
______________________________________ 
5-octoxy-2-(4-decoxyphenyl)pyrimidine 
20 mol-% 
5-octoxy-2-(4-octoxyphenyl)pyrimidine 
11 mol-% 
5-octoxy-2-(4-hexoxyphenyl)pyrimidine 
24 mol-% 
5-octoxy-2-(4-butoxyphenyl)pyrimidine 
25 mol-% 
##STR46## 9 mol-% 
4-hexoxyphenyl 4'-decoxybenzoate 
(= compound of the general formula VII) 
##STR47## 11 mol-% 
4-hexoxyphenyl 4-octoxybenzoate 
(compound of the general formula VII) 
has the following liquid-crystalline ranges: 
X 6 S.sub.c 72.3 S.sub.A 85.2 N 92 I 
______________________________________ 
b) A four-component mixture which differs from the liquid-crystal mixture 
16a only in that it contains no compound of the general formula (VII) has 
the following liquid-crystalline phase ranges: 
______________________________________ 
X 13 S.sub.c 81.5 
S.sub.A 95.5 
N 98 I 
______________________________________ 
Compared with the mixture 16b, the mixture 16a according to the invention 
has a melting point which is lower by 7.degree. C. and a upper S.sub.c 
phase-range limiting temperature which is lower by 9.degree. C. 
Example 17 
A ferroelectric mixture comprising the following components 
__________________________________________________________________________ 
mixture from Example 3a 82 mol-% 
##STR48## 3 mol-% 
Racemate of 4-(2-nonoxypyrimidin-5-yl)phenyl 
2-chloro-4-methylpentanoate 
##STR49## 9 mol-% 
4-pentylphenyl 4'-hexoxybenzoate 
(compound of the general formula VIII) 
##STR50## 
4-(2-nonoxypyrimidin-5-yl)phenyl (2S,3S)- 
6 mol-% 
2-chloro-3-methylpentanoate 
has the following LC ranges: 
X -9 S.sub.c * 61 S.sub.A * 70 N* 85 I 
__________________________________________________________________________ 
At 20.degree. C., this mixture has a polarization of -8.2 nC cm.sup.-2, a 
contrast of 5.7 and, in a switching field of 10 V.mu.m.sup.-1, a switching 
time of 54 .mu.s. Comparison with the mixture from Example 12b confirms 
that the addition of the ester of the general formula (VIII) reduces the 
melting point by 4.degree. C. and increases the contrast by 24%. 
Example 18 
a) A liquid-crystalline mixture comprising the following nine components 
______________________________________ 
5-octoxy-2-(4-hexoxyphenyl)pyrimidine 
14 mol-% 
5-octoxy-2-(4-octoxyphenyl)pyrimidine 
5 mol-% 
5-octoxy-2-(4-butoxyphenyl)pyrimidine 
15 mol-% 
5-octoxy-2-(4-decoxyphenyl)pyrimidine 
8 mol-% 
5-octoxy-2-(4-dodecoxyphenyl)pyrimidine 
8 mol-% 
5-octyl-2-(4-dodecoxyphenyl)pyrimidine 
13 mol-% 
[4-(5-decylpyrimidin-2-yl)]phenyl 
17 mol-% 
trans-4-pentylcyclohexanecarboxylate 
##STR51## 13 mol-% 
4-(5-octylpyrimidin-2-yl)phenyl heptanoate 
(= compound of the general formula V) 
##STR52## 7 mol-% 
4-(10-decylpyrimidin-2-yl)phenyl undecanoate 
(compound of the general formula V) 
exhibits the following liquid-crystalline phase ranges: 
X -3 S.sub.c 73 S.sub.A 81 N 94 I 
______________________________________ 
b) A comparable mixture which differs from the mixture 18A only in that it 
contains no component of the general formula (V) has the following 
liquid-crystalline phase ranges: 
______________________________________ 
X -1 S.sub.c 81 
S.sub.A 87 
N 103 I 
______________________________________ 
The mixture according to the invention thus has a melting point which is 
lower by 2.degree. C. and an upper S.sub.c phase-range limiting 
temperature which is lower by 8.degree. C. 
Example 19 
A ferroelectric liquid-crystalline mixture comprises the following ten 
components 
______________________________________ 
5-octoxy-2-(4-butoxyphenyl)pyrimidine 
13.2 mol % 
5-octoxy-2-(4-hexoxyphenyl)pyrimidine 
14 mol % 
5-octoxy-2-(4-octoxyphenyl)pyrimidine 
5.5 mol % 
5-octoxy-2-(4-decoxyphenyl)pyrimidine 
7 mol % 
5-octoxy-2-(4-dodecoxyphenyl)pyrimidine 
7 mol % 
[4-(5-decylpyrimidin-2-yl)]phenyl trans- 
16.7 mol % 
4-pentylcyclohexanecarboxylate 
5-octyl-2-(4-dodecoxyphenyl)pyrimidine 
11.4 mol % 
[4-(5'-octylpyrimidin-2-yl)]phenyl heptanoate 
13.2 mol % 
4-(2-nonoxypyrimidin-5-yl)phenyl 2-fluoro- 
6 mol % 
4-methylpentanoate 
(compound of the general formula IX) 
4-(2-nonoxypyrimidin-5-yl)phenyl (2S,3S)- 
6 mol % 
2-chloro-3-methylpentanoate 
exhibits the following liquid-crystalline phase ranges: 
X -8 S.sub.c * 73 
S.sub.A * 80 
N* 90 I 
______________________________________ 
and has, at 25.degree. C., a spontaneous polarization of 9.4 nC cm.sup.-2, 
a contrast of 5.8 and a switching time of 65 .mu.s. 
By comparison, the claimed ferroelectric FLC mixture from Example 7a, which 
differs from the abovementioned ferroelectric mixture only in that it 
contains no racemate (IX), has the following phase ranges: 
______________________________________ 
X -1 S.sub.c * 80 
S.sub.A * 85 
N* 99 I 
______________________________________ 
In comparison, the abovementioned ferroelectric mixture has a melting point 
which is lower by 7.degree. C. 
Example 20 
a) A liquid-crystalline mixture comprising the following six components 
______________________________________ 
5-oxtoxy-2-(4-hexoxyphenyl)pyrimidine 
20.2 mol-% 
5-octoxy-2-(4-octoxyphenyl)pyrimidine 
9.4 mol-% 
5-octoxy-2-(4-butoxyphenyl)pyrimidine 
21.4 mol-% 
5-octoxy-2-(4-decoxyphenyl)pyrimidine 
17 mol-% 
[4-(5-decylpyrimidin-2-yl)]phenyl 
12 mol-% 
trans-4-pentylcyclohexanecarboxylate 
##STR53## 20 mol-% 
[4-(5'-octoxypyrimidin-2-yl)]phenyl decanoate 
(= compound of the general formula VI) 
exhibits the following liquid-crystalline phase ranges: 
X 8 S.sub.c 80 S.sub.A 92 N 100 I 
______________________________________ 
b) The following mixture, which is claimed in DE 3,831,2265.3 and differs 
from the mixture 20a only in that it contains no component of the general 
formula (VI), is suitable for comparison of the physical properties. This 
mixture comprising five components has the following liquid-crystalline 
phase ranges: 
______________________________________ 
X 10 S.sub.c 84 
S.sub.A 93 
N 105 I 
______________________________________ 
In comparison with the mixture lb, the mixture 20a according to the 
invention has a melting point (X) which is lower by 2.degree. C. and an 
upper S.sub.c phase-range limiting temperature which is lower by 4.degree. 
C.