九州大学大学院総合理工学府報告第 41 巻 第 2 号 1-11 頁 令和 2 年 2 月

Engineering Sciences Reports, Kyushu University
Vol. 41, No. 2, pp. 1-11, FEB, 2020

Initial Product-Ion Distributions in Ion-Molecule
Reactions of CH5+, C2H5+, and C3H5+ with PhX(X = H, CH3, C2H5, C2H3, and C2H)
Masaharu TSUJI*1,2† Takeshi ARIKAWA*3 Keiko UTO*1
Jun-Ichiro HAYASHI*1,2 and Takeshi TSUJI*4
E-mail of corresponding author: tsuji@cm.kyushu-u.ac.jp†(Received August 26, 2019, accepted September 9, 2019)
The gas-phase ion-molecule reactions of CH5+, C2H5+, and C3H5+ with five monosubstituted
benzenes (M = PhX: X = H, CH3, C2H5, C2H3, and C2H） have been investigated under a reactant-ion
selective mode of an ion-trap type of GC/MS. The dependence of product-ion distributions on the reaction
time indicated that collisional stabilization takes part in the formation of such adduct ions as (M +C2H5)+, (M + C3H5)+, and (M + C3H5 – C2H4)+. It was found that radiative association also participatesin the formation of (M + C3H5)+ adduct ion for M = PhC2H. The initial product-ion distributions were
determined by extrapolating the dependence of branching ratios of product ions on the reaction timeto zero reaction time. The reaction mechanisms were discussed based on initial product-ion
distributions and heats of reactions of each product channel estimated from semi-empirical quantum
calculations.
Key words: Hydrocarbon ions, Benzene derivatives, Aromatic hydrocarbons, Chemical ionization,
Ion trap type GC/MS, Collisional stabilization, Radiative association

1.

Introduction

We have made a systematic massspectrometric study on ion-molecule reactionsof such typical hydrocarbon ions as CH5+, C2H5+,
and C3H5+ with mono-substituted benzenes
using an ion-trap type of GC/ MS.1-7) In aprevious paper for aromatic hydrocarbons,results for PhX (X = H and CH3) have beenreported.1) The reaction mechanisms of these
two typical aromatic hydrocarbons for the threehydrocarbon ions were discussed based on
product-ion distributions and heats of reactions
in each product channel.
We discussed reaction mechanisms of PhX (X= H and CH3) for CH5+, C2H5+, and C3H5+ ions on
the basis of product-ion distributions measured
at a constant reaction time of 20 ms, assumingthat the effects of secondary collisions were*1

Institute for Materials Chemistry and Engineering,and Research and Education Center of GreenTechnology*2 Department of Applied Science for Electronics andMaterials*3 Department of Applied Science for Electronics andMaterials, Graduate Student*4 Department of Materials Science, Shimane
University

insignificant. However, we have noticed that
this assumption is incorrect, because total
number of collisions of a product ion withchemical ionization (Cl) CH4 gas is estimated to
be about 50 times at 20 ms on the basis of asimple hard sphere gas kinetic model.
Therefore, collisional stabilization may
participate in the formation of product ions.
In the present study, we have reinvestigated
the ion-molecule reactions of CH5+, C2H5+, andC3H5+ ions with PhX (X = H and CH3). In
addition, reactions with PhX (X = C2H5, C2H3,
and C2H) are investigated in order obtain moredetailed information on substitution effects ofbenzene mono-derivatives having saturated
and
unsaturatedhydrocarbons.
The
dependence of product-ion distribution on thereaction time is measured in order to examine
the contribution of collisional stabilization to
the formation of each product ion. The initial
product-ion distributions are estimated byextrapolating the dependence of branchingratios of product ions on the reaction time tozero reaction time. The reaction mechanisms
are discussed based on initial product-ion
distributions and thermochemical calculations

Ion-molecule reactions of RH+ with aromatic hydrocarbons

2

were evaluated to be 10 and 4.2 eV for CH5+, 6.0
and 2.4 eV for C2H5+, and 4.3 and 1.7 eV forC3H5+, respectively, using a pseudo-potential
well method.9) These energies are higher thanthat in the medium-pressure CI experiments,
which was estimated to be less than 1 eV.10)
The time for storing a reactant ion was 5 ms.
The reaction time was varied from 1 to 100 ms.
The ion-trap cell was kept at ≤170 oC. The
reagents were diluted in hexane and injected
into the GC with a high-purity carrier He gas.
The partial pressures of He and CH4 in an iontrap cell were estimated to be 5 × 10-5 and 7 ×
10-5 Torr, respectively. The mass spectra were
measured at low reagent concentrations ofabout 1000–10000 pg cm-3 in order to remove
secondary ion-molecule reactions with reagent
molecules.

of heats of reactions using a semi-empirical
PM3 method.

2.

Experimental

CH4 CI mass spectra were obtained using an
ion-trap type of Hitachi M7200 GC/MS in areactant-ion selective mode. The electronimpact ionization on CH4 provides primary
CHn+ (n = 2–4) ions, and the subsequent fastion-molecule reactions yield the secondary
CH5+, C2H5+, and C3H5+ ions with chemical
structures given in Fig. 1:8)
CH4+ + CH4 → CH5+ + CH3
CH3+ + CH4 → C2H5+ + H2
CH2+ + CH4 → C2H3+ + H2 + H
C2H3++ CH4 → C3H5+ + H2.

CH5+
H

++

H

H

H

H

3.

Results and discussion

C2H5+

C3H5+

H

H

3.1 Summary of Mass Spectroscopic DataCThe observed product ions, their reactiontime dependence, and initial product-ion
distributions in each reaction are summarizedin Table 1. The branching ratios of product ionseither increase, decrease, or unchanged withincreasing the reaction time. They are
represented by +, –, and 0, respectively, inbrackets in Table 1. The initial product-ion
distributions were estimated by extrapolating
the dependence of branching ratios of productions on the reaction time to zero reaction time.
The uncertainties of the branching ratios were
estimated to be within ±7%.

H

C

(1)
(2)
(3a)
(3b)

C

+

C

H

H H C
H
H

+ C H
H

Fig. 1. Chemical structures of CH5+, C2H5+,
and C3H5+ ions.
Since further reactions of CH5+, C2H5+, andC3H5+ with CH4 are very slow, these ionsbecome dominant reactant ions in the CH4 CI
experiments. The reactant CH5+, C2H5+, orC3H5+ ion was selectively trapped in the ion
trap. The maximum and average kinetic
energies of the reactant ions in our apparatus

Table 1. Branching ratios (%) of product ions produced from reactions of CH5+, C2H5+, and C3H5+
ions with PhX (X = H, CH3, C2H5, C2H3, and C2H).a)
Reagents
Reactant ions

PhCH3

PhH
CH5

+

+

+

CH5

66(+)

100

C2 H5 C3 H5++

PhC2H5

C2H5 C3 H5

+

CH5

+

PhC2H3

+

+

PhC2H

+

CH5

+

C2 H5 C3 H5

+

CH5

+

C2H5 C3 H5

48(-)

100

83(-) 44(-)100

92(-) 49(-)

C2 H5 C3 H5++

Product Ions+

(M + H)(M + H - CH4)+

100

100

100

71(-)

(M + H - C2 H4 )+

58(+)
0(+)

100

42(-)

(M + C2 H5 )+

0(+)

0(+)

(M + C2 H5 - C3 H4 )+8(+)(M + C2 H5 - C3 H6 )+17(-)(M + C3 H5 )+

0(+)

0(+)

0(+)

(M + C3 H5 - CH3 )+(M + C3 H5 - C2 H4 )+(M + C3 H5 - C4 H4 )

34(-)

26(+)

40(+)

4(-)
6(-)

+

+

0(+)

+

(M + C3 H5 - C4 H6)(M - H)

6(+)
35(+)

56(-)
3(+)

12(0)

a) Symbols, +, –, and 0 in brackets denote its branching ratio increases, decreases, or

unchanges with increasing the reaction time, respectively.

令和元年度

第 41 巻九州大学大学院総合理工学報告

3.2 Benzene (PhH)(1a) Protonation
-R

+ RH+

1
(1b) Association+ C3H5+CH2- C2H4

+ CH4
－h

2

0.8

C3H5

,

3

4

Scheme 1. Possible reaction pathways for theion-molecule reactions of RH+ (R = CH4,
C2H4, and C3H4) with PhH.
In order to examine the contribution ofcollisional stabilization, the dependence of
product-ion distributions on the reaction time
was measured in the C3H5+/PhH reaction (Fig.
2). The branching ratio of (M + C3H5 – C2H4)+
ion decreases with increasing the reaction time.
This indicates that collisional stabilization does
not participate in the formation of (M + C3H5 –C2H4)+. In general, effects of collisional
stabilization is small for PT reactions. However,an increase in the branching ratio of (M + H)+
ion with increasing the reaction time suggeststhat collisions with CI CH4 gas slightly
contributes to the formation of (M + H)+ ion in
the C3H5+/PhH reaction.

0.6(M + H)+(M + C 3H5 - C2H4)+

0.4
0.2
0.0

0

20

40
60
80
Reaction time (ms)100

Fig. 2. Dependence of branching ratios ofproduct ions on the reaction time in the
C3H5+/PhH reaction.
The (M + C3H5 – C2H4)+ ion is produced
through dissociative association by loss of C2H4
[Scheme (1b)]. There are two possible productsfor (M + C3H5 – C2H4)+ ion as shown in 3
(PhCH2)+ and 4 (C7H7+) in Scheme (1b). On thebasis of energy calculations (Table A1(Appendix)), the heat of reaction for theformation of 4 (C7H7+) is lower than that of 3
(PhCH2+) by 0.53 eV. Therefore, 4 (C7H7+) will
be a major product ion as (M + C3H5 – C2H4)+.
3.3

H

3

1.0

Branching ratios

In the CH5+/PhH and C2H5+/PhH reactions,only (M + H)+ ion is observed. In the C3H5+/PhH
reaction, besides a major (M + H)+ ion with abranching ratio of 66%, (M + C3H5 – C2H4)+ ion
is observed as a minor ion (34%). Possible
reaction pathways for the RH+/PhH reactions
are shown in Scheme 1. Collisional
stabilization and radiative association canparticipate in the association reactions. They
are shown using such symbols as +CH4 and–h, respectively, in Scheme 1.
The (M + H)+ ion is formed through protontransfer (PT) [Scheme (1a)], which are 0.05–
2.16 eV exothermic on the basis of energy
calculations (Table A1 (Appendix)). In general,the proton-donating ability (acidity) ofhydrocarbon ions decreases with increasing thedissociation energy of RH+ → R + H+, which isdenoted as D0(R–H+). Since the D0(R–H+) value
increases in the order of CH5+ (5.7 eV), C2H5+(7.1 eV), and C3H5+ (7.83 eV for
CH2=CHCH2+),11) the acidity of hydrocarbon
ions decreases in the same order. One reason
for the small branching ratio of the PT channel
in the C3H5+/PhH reaction is the weakest
acidity of the C3H5+ ion.

第2号

Toluene (PhCH3)

Only PT channel leading to (M + H)+ [Scheme(2a)] is found in the CH5+/PhCH3 andC2H5+/PhCH3 reactions. It should be noted thatin addition to the (M + H)+ ion, (M + C3H5)+ and(2a) Protonation
CH3

CH3

o- 5a
m- 5b
p- 5c
i- 5d

-R

+

+ RH

H

(2b) Association
CH3

CH3
+

+ C3 H5－h(2c) H－ Abstraction

CH3

CH3

- C2H4

+ CH4

C3H5
o- 6a
m- 6b
p- 6c
i- 6d

o- 7a
m- 7b
p- 7c

CH2 ,

8

CH2

CH3
+

- C3H6+ C3H5,

9

10

Scheme 2. Possible reaction pathways forthe ion-molecule reactions of RH+ (R = CH4,
C2H4, and C3H4) with PhCH3.

Ion-molecule reactions of RH+ with aromatic hydrocarbons

4(M + C3H5 – C2H4)+ ions arising fromassociation reactions [Scheme (2b)] and (M –H)+ ion resulting from the hydride ion
abstraction reaction [Scheme (2c)] are observedin the C3H5+/PhCH3 reaction.
It is known that three-body collisional
association and two-body radiative association
can participate in the formation of adductions.12,13) In radiative association, adduct ions
are stabilized by radiating infrared emissions.
A typical rate of infrared emission would be 100
photons s-1, whereas the total collision numbersin this study are estimated to be 2–240 times
during reaction times of 1–100 ms,
corresponding to the collision rate of 2400
collisions s-1. Therefore, not only radiative
association (–h) but also collisional association(+CH4) may participate in the formation of (M+ C3H5)+ under our operating conditions.
Fig. 3 shows the dependence of branchingratios of product ions on the reaction time in
the C3H5+/PhCH3 reaction. The branchingratios of (M + C3H5)+ and (M + C3H5 – C2H4)+
ions increase, as the reaction time increases.
These
results
imply
that
collisional
stabilization takes part in the formation of (M+ C3H5)+ and (M + C3H5 – C2H4)+ ions. The
disappearance of (M + C3H5)+ ion at zeroreaction time indicates that this adduct ion is
exclusively produced by collisional stabilization
and radiative association does not contribute to
the formation of (M + C3H5)+. The branchingratio of the (M – H)+ ion slightly increases withincreasing the reaction time, suggesting thatcollisional stabilization takes part in theformation of (M – H)+.

The major (M + H)+ ions (5a–5d) with
branching ratios of 71–100% are formed
through an attack on the benzene ring [Scheme(2a)]. Minor (M + C3H5 – C2H4)+ and (M – H)+ions with branching ratios of 26 and 3%,
respectively, are formed through dissociative
association [Scheme (2b)] and H– abstraction[Scheme (2c)]. Molecular structures 7 and 8 are
possible as (M + C3H5 – C2H4)+ ions, whereas
molecular structures 9 and 10 are possible as(M – H)+. On the basis of energy calculations
given in Table A1 (Appendix), tropylium typeions 8 and 10 are energetically favorable
products. Therefore, they will be dominant
product ions.
3.4

Ethylbenzene (PhC2H5)

Major product channels for PhC2H5 is PT as
in the cases of PhH and PhCH3 [Scheme (3a)].
Although only non-dissociative PT channel isobserved in the CH5+/PhH and CH5+/PhCH3
reactions, not only non-dissociative PT channel(58%) but also dissociative PT channels leadingto (M + H – CH4)+ and (M + H – C2H4)+ (42%)
are found in the CH5+/PhC2H5 reaction [Scheme(3a)]. In the C2H5+/PhC2H5 and C3H5+/PhC2H5
reactions, only non-dissociative PT channel isfound. In the C3H5+/PhC2H5 reaction, besides
non-dissociative PT channel with a branchingratio of 48%, association reactions leading to (M+ C3H5)+ and (M + C3H5 – C2H4)+ ions and H–
abstraction reaction leading to (M – H)+ ion are(3a) Protonation

CH2
- CH4

C2H5

Branching ratiosHo- 11am- 11bp- 11ci- 11d(M + H)+

0.8(M + C3H5 - C2H4)+
C2H5(M - H) +

+

C2H5

C2H5

- C2H4－hC3H5o- 15am- 15bp- 15ci- 15d

0.2

H

14

+ CH4

0.4

o- 16am- 16bp- 16cCH2 ,17(3c) H－ Abstraction
C2H5

0.0

H

C2H5
+ C3H513- C2H4(3b) Association(M + C3H5)+

0.6

12

-R

+ RH+

1.0

,

C2H5

0

20

40
60
80
Reaction time (ms)100

Fig. 3. Dependence of branching ratios ofproduct ions on the reaction time in the
C3H5+/PhCH3 reaction.

CHCH3+ C3H5+

CH3- C3H6,
18

19

Scheme 3. Possible reaction pathways forthe ion-molecule reactions of RH+ (R = CH4,
C2H4, and C3H4) with PhC2H5.

令和元年度

九州大学大学院総合理工学報告

observed with total branching ratios of 40 and
12%, respectively [Scheme (3b) and (3c)].
Figs. 4a and 4b show the dependence ofbranching ratios of product ions on the reaction
time in the CH5+/PhC2H5 and C3H5+/PhC2H5
reactions, respectively. In the CH5+/PhC2H5
reaction, the branching ratios of (M + H)+ and(M + H – CH4)+ increase, whereas that of (M +H – C2H4)+ decreases with increasing thereaction time. These results imply thatcollisional stabilization take part in theformation of the former ions. At zero reaction
time, the branching ratio of (M + H – CH4)+ iszero, indicating that it is exclusively formed
via collisional stabilization.
In the C3H5+/PhC2H5 reaction, the branchingratios of (M + C3H5)+ and (M + C3H5 – C2H4)+
ions increase with increasing the reaction time.
Although the branching ratio of the (M + C3H5)+
ion decreases to zero as the reaction timedecreases to zero, that of the (M + C3H5 – C2H4)+
ion converges into a high value of 40% at zero

(a)

1.0
(M + H - CH4)+

Branching ratios

0.8(M + H - C 2H4)+

0.6
0.4
0.2
0.0

(b)

0

10

20
30
40
Reaction time (ms)50

1.0
(M + H)+(M - H)+

0.8
Branching ratios(M + C3H5- C2H4)+(M + C3H5)+

0.6
0.4
0.2
0.0

0

20

40

60

80

100

Reaction time (ms)Fig. 4. Dependence of branching ratios ofproduct ions on the reaction time in the (a)CH5+/PhC2H5 and (b) C3H5+/PhC2H5
reactions.

第2号

5reaction time. On the basis of these findings, it
was concluded that the adduct (M + C3H5)+ ion
isproducedonly
throughcollisional
stabilization, whereas most of the (M + C3H5 –C2H4)+ ion is formed through without thecontribution of collisional stabilization.
In Scheme 3 are shown observed major
reaction pathways of the RH+/PhC2H5 reactions.
The (M + H)+, (M + H – CH4)+, (M + H – C2H4)+,(M + C3H5)+, and (M + C3H5 – C2H4)+ ions areformed through electrophilic attack on thebenzene ring [Scheme (3a) and (3b)], whereas(M – H)+ ion is formed by H– abstraction fromthe C2H5 group [Scheme (3c)]. The chemical
structure of (M + C3H5 – C2H4)+ is 14. Twochemical structures, 12 and 13, 16 and 17, and18 and 19, are possible for the (M + H – CH4)+,(M + C3H5 – C2H4)+, and (M – H)+ ions,
respectively. In all cases, tropylium type ions13, 17, and 19 are more favorable on the basisof energy calculations (Table A1 (Appendix)). It
is therefore reasonable to assume that theseare major product ions.
3.5(M + H)+第 41 巻Styrene (PhC2H3)

Only PT reaction [Scheme (4a)] is observed intheCH5+/PhC2H3
reaction.
In
the
C2H5+/PhC2H3 reaction, the dominant productchannel (83%) is PT. In addition, association
reactions leading to (M + C2H5)+ and (M + C2H5
– C3H6)+ ions are observed with a total
branching ratio of 17% [Scheme (4b)]. In the
C3H5+/PhC2H3 reaction, the dominant productchannel (56%) is the dissociative association
leading to (M + C3H5 – C4H6)+ ion, and the restof the product channel (44%) is PT.
Figs. 5a and 5b show the branching ratios ofproduct ions on the reaction time in the
C2H5+/PhC2H3 and C3H5+/PhC2H3 reactions,
respectively. In Fig. 5a, the branching ratio of(M + C2H5)+ increases with increasing thereaction time. Its branching ratio becomes zeroat zero reaction time, indicating that (M +C2H5)+ is selectively formed by collisional
stabilization. In Fig. 5b, the branching ratio of(M + C3H5 – C4H6)+ slightly decreases withincreasing the reaction time. Therefore, most of
this ion is formed without effects of collisional
stabilization. Although other association
channels leading to (M + C3H5)+ and (M + C3H5
– C2H4)+ are found in the C3H5+/PhC2H3
reaction, their branching ratios are zero at zeroreaction time. On the basis of these findings,
the adduct (M + C3H5)+ and (M + C3H5 – C2H4)+

Ion-molecule reactions of RH+ with aromatic hydrocarbons

6(4a) Protonation

(a)

CH3

HC CH30.8,

20Branching ratios

21
CH3

H2C CH2

CH CH2
-R

+

+ RH

1.0

,

22

21

CH CH2H

0.6(M + H)+(M + C2H5 - C3H6)+

0.4(M + C2H5)+

0.2

o- 23am- 23bp- 23ci- 23d

0.0

0

20

40

60

80

100

40
60
80
Reaction time (ms)100

Reaction time (ms)(4b) Association

CH CH2 C2H5(b)
CH2
- C 3H 6+ + CH4

,

－h

25

27

HC CH2C2H529
HC CH2

C3H5- C2 H 4

CH CH2

HC CH2
HC CH2o- 32am- 32bp- 32c
,
CH2

33

CH2

30

- C4 H6

HC CH2,27

o- 31am- 31bp- 31ci- 31d(M + C 3H5 - C2H4)+

0.6
0.4

0.0

+ CH4
－h

(M + C 3H5)+

0.2

o- 26am- 26bp- 26ci- 26d
CH CH2 C3H5(4c) Association+ C 3 H5 +28

Branching ratios+ C 2H 5

H
C CH2

C2H5

(M + H)+(M + C 3H5 - C4H6)+

0.8

24
HC CH2

1.0

28

C3H5

Scheme 4. Possible reaction pathways for theion-molecule reactions of RH+ (R = CH4, C2H4,
and C3H4) with PhC2H3.
ions are produced only through collisional
stabilization.
In Scheme (4a)–(4c) are shown the observed
major reaction pathways of the RH+/PhC2H3
reactions. The (M + H)+, (M + C2H5)+, (M + C2H5
– C3H6)+, (M + C3H5)+, (M + C3H5 – C2H4)+, and(M + C3H5 – C4H6)+ ions are formed throughelectrophilic attack on the benzene ring and/or
the vinyl group. On the basis of energy diagramof these products (Table A1 (Appendix)),

020

Fig. 5. Dependence of branching ratios ofproduct ions on the reaction time in the (a)C2H5+/PhC2H3
and(b)
C3H5+/PhC2H3
reactions.
electrophilic attack of H+, C2H5+, and C3H5+ on
the vinyl group is favorable. Therefore,
tropylium type ions, 21 in Scheme (4a), 28 in
Scheme (4b), and 33 and 28 in Scheme (4c)formed via electrophilic attack of reactant ionson the vinyl group will be dominant products.
In Scheme (4a), (4b), and (4c), chemical
structures 20, 25, and 30 are more stable than22, 24, and 29. Therefore, they will be major
initial protonated and adduct ions before
isomerization and elimination of C3H6, C2H4,
and C4H6.
3.6 Phenylacetylene (PhC2H)
Only PT reaction is observed in theCH5+/PhC2H reaction [Scheme (5a)]. In the
C2H5+/PhC2H reaction, the major productchannel (92%) is also PT. In addition, (M +C2H5)+ and (M + C2H5 – C3H4)+ ions areobserved as minor products. In the
C3H5+/PhC2H reaction, about half of thereaction (49%) is PT and the rest of the half

令和元年度

九州大学大学院総合理工学報告(5a) Protonation

第 41 巻

HC CH

第2号

7

1.0

(a)
0.8

C CH

Branching ratios

34
C CH2
-R

+ RH+

35
C

CH

(M + C2H5 - C3H4)+(M + C2H5)+

0.4
0.2

o- 36am- 36bp- 36ci- 36dH(M + H)+

0.6

0.0

0

20

40

60

80

100

40
60
80
Reaction time (ms)100

Reaction time (ms)C CH C2H5(5b) Association

1.0

(b)
0.8

C2H5

+ C2H5+

C CH

+ CH4

CH2
- C3 H 4

－h

,

38

40

41

C CH

C2H5

C CH
+ C3H5+

C3H5

45
C CH

C CH

C CH

+ CH4

- C2H4

－h

CH2

43
C CH

o- 46am- 46bp- 46c,47

CH2- C4H4o- 44am- 44bp- 44ci- 44d

C3H5

,

40

(M + C 3H5 - C2H4)+(M + C 3H5 - CH3)+

0.6
0.4

0.0

- CH3

42

(M + C 3H5)+

0.2

o- 39am- 39bp- 39ci- 39dC CH C3H5(5c) Association

Branching ratios

37
C CH

(M + H)+(M + C 3H5 - C4H4)+41

Scheme 5. Possible reaction pathways for theion-molecule reactions of RH+ (R = CH4, C2H4,
and C3H4) with PhC2H.
reaction (51%) is the non-dissociative anddissociative association leading to (M + C3H5)+,(M + C3H5 – CH3)+, (M + C3H5 – C2H4)+, and (M+ C3H5 – C4H4)+. Among them, the (M + C3H5 –C2H4)+ ion is a dominant ion (35%).
Figs. 6a and 6b show the dependence of
product ions on the reaction time in the
C2H5+/PhC2H and C3H5+/PhC2H reactions,
respectively. Although the branching ratio of(M + C2H5)+ ion increases with increasing thereaction time, it is zero at zero reaction time.

020

Fig. 6. Dependence of branching ratios ofproduct ions on the reaction time in the (a)C2H5+/PhC2H and (b) C3H5+/PhC2H reactions.
Therefore the (M + C2H5)+ ion is exclusively
formed though the collisional stabilization. The
branching ratio of (M + C2H5 – C3H4)+ at zeroreaction time is 8%, indicating that this ion isformed without assistance of collisional
stabilization. Fig. 6b indicates that thecollisional stabilization takes part in theformation of (M + C3H5)+ and (M + C3H5 – CH3)+
ions. It should be noted that the branching ratioof (M + C3H5)+ is not zero but 6% at zeroreaction time. This implies that a small amountof (M + C3H5)+ ion is formed through radiative
association.
In Scheme 5 are shown the observed major
reaction pathways of the RH+/PhC2H reactions.
The (M + H)+, (M + C2H5)+, (M + C2H5 – C3H4)+,(M + C3H5)+, (M + C3H5 – CH3)+, (M + C3H5 –C2H4)+, and (M + C3H5 – C4H4)+ ions are formed
through electrophilic attack on the benzene
ring and/or the ethynyl group. On the basis ofenergy diagram of these product channels(Table A1 (Appendix)), electrophilic attack of
H+, C2H5+, and C3H5+ on the ethynyl group isIon-molecule reactions of RH+ with aromatic hydrocarbons

8

Table 2. Branching ratios (%) of each product channel in reactions of CH5+, C2H5+, and C3H5+ ionswith PhX (X = H, CH3, C2H5, C2H3, and C2H).
Reagents
Reactant ionsProtonation
Association

PhH
CH5 + C2 H5 + C3 H5 +non-dissociative 100 100
66
dissociative
non-dissociative
dissociative
34

PhCH3

PhC2H5

PhC2H3PhC2H

CH5 + C2 H5 + C3 H5 +100 100
71

CH5 + C2 H5 + C3 H5+
58
100
48
42

CH5 + C2 H5 + C3 H5 +
100
83
44

CH5 + C2 H5 + C3 H5 +
100
92
49

17

8

-

H - Abstraction

favorable. Therefore, major (M + H)+, (M +C2H5)+, and (M + C3H5)+ ions will be 35 in
Scheme (5a), 37 in Scheme (5b), and 42 in
Scheme (5c). Two chemical structures 40 and
41 are possible as (M + C3H5 – C3H4)+. Since theformation of tropylium type ion 41 isenergetically more favorable (Table A1(Appendix)), it will be a dominant product. The(M + C3H5 – CH3)+ ion will be a stable
naphthalene ion 45. Although two chemical
structures 46 and 47 are possible as (M + C3H5
– C2H4)+, whereas chemical structures 40 and
41 are possible as (M + C3H5 – C4H4)+, morestable tropylium type ions 47 and 41 will bemajor product ions.

4.

Summary and Conclusion

The gas-phase ion-molecule reactions of CH5+,
C2H5+, and C3H5+ with five monosubstituted
benzenes (M = PhX: X = H, CH3, C2H5, C2H3,
and C2H) have been investigated under areactant-ion selective mode of an ion-trap typeof GC/MS at a low CH4 pressure. The
dependence of product-ion distributions on thereaction time indicated that collisional
stabilization takes part in the formation of such
adduct ions as (M + C2H5)+, (M + C3H5)+, and (M+ C3H5 – C2H4)+. It was found that radiative
association also participates in the formation ofthe (M + C3H5)+ adduct ion for M = PhC2H.
The branching ratios of protonation,
association,
andH–
abstraction
aresummarized in Table 2. In the CH5+ reactions,only PT was found. In the CH5+/PhC2H5
reaction, not only non-dissociative PT (58%) but
also dissociative PT (42%) was observed. In the
C2H5+/PhX (X = H, CH3, C2H5) reactions, only
non-dissociative PT was observed. In the
C2H5+/PhX (X = C2H3 and C2H) reactions,dominant product channel (83–92%) was also
non-dissociative PT. In addition, small
amounts of dissociative association channels(8–17%) leading to tropylium type ions wereobserved. The occurrence of association
reactions in the C2H5+/PhX (X = C2H3 and C2H)
reactions can be attributed the fact that the

26

40

3

12

56

6
45

electrophilic attach of C2H5+ on unsaturated
C2H3 and C2H groups is energetically favorable.
In the C3H5+ reactions, non-dissociative PT
occupied 44–71%, and non-dissociative anddissociative association occupied 26–56%. In
the C3H5+/PhX (X = CH3 and C2H5) reactions,H– abstraction channels were observed asminor processes (3–12%).
In all reactions, PT reactions were observed.
For the cases of PhX (X = H, CH3, and C2H5),
protonation occurs on a benzene ring. On theother hand, PT reactions can take place both ona benzene ring and a substituent for the casesof PhX (X = C2H3 and C2H). On the basis ofenergetics, protonated ions formed by an attackon the substituent is more favorable. Therefore,
PT reactions dominantly occur on thesubstituent.
References
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)

12)
13)

M. Tsuji, E. Oda, and Y. Nishimura, Chem. Lett., 26,
781 (1997).
M. Tsuji and Y. Nishimura, Bull. Chem. Soc. Jpn., 71,
273 (1998).
M. Tsuji, K. Arikawa, and Y. Nishimura, Bull. Chem.
Soc. Jpn., 72, 293 (1999).
M. Tsuji, T. Arikawa, and Y. Nishimura, Bull. Chem.
Soc. Jpn., 73, 131 (2000).
M. Tsuji, T. Arikawa, Y. Tanaka, and Y. Nishimura,
Bull. Chem. Soc. Jpn., 73, 1673 (2000).
M. Tsuji, T. Arikawa, Y. Tanaka, K. Mogi, and Y.
Sakai, J. Mass Spectrom. Soc. Jpn., 49, 188 (2001).
T. Arikawa and M. Tsuji, J. Mass Spectrom. Soc. Jpn.,
59, 69 (2011).
F. H. Field and M. S. B. Munson, J Am. Chem. Soc.,
87, 3289 (1965).
J. F. J. Todd, R. M. Waldren, and R. F. Bonner, Int. J.
Mass Spectrom. Ion Phys., 34, 17 (1980).
C. Chang, G. G. Meisels, and J. A. Taylor, Int. J.
Mass Spectrom. Ion Phys., 12, 411 (1973).
S. G. Lias, J. E. Bartmess, J. F. Liebman, J. L. Holmes,
R. D. Levin, and W. G. Mallard, J. Phys. Chem. Ref.
Data, 17, Suppl. 1 (1988); updated data were obtained
from NIST Standard Ref. Database, Number 69, 2018(http://webbook.nist.gov/chemistry).
R. C. Dunbar, Int. J. Mass Spectrom. Ion Process., 100,
423 (1990).
G. Weddle and R. C. Dunbar, Int. J. Mass Spectrom.
Ion Process., 134, 73 (1994).

令和元年度

九州大学大学院総合理工学報告第 41 巻第2号

9

Appendix
Table A1. Heats of reactions of each product channel (in eV Units).a)
ΣΔH0
ΣΔH0
Reactants

ΔH0

Reactants

Products

Products

Reactionsb)

CH5+ + PhH
C2H5+ + PhH
C3H5+ + PhH

10.23
10.21
10.66

CH5+ + PhCH3

9.89

C2H5+ + PhCH3

9.87

C3H5+ + PhCH3

10.32

CH5+ + PhC2H5

9.67

C2H5+ + PhC2H5

9.65

C3H5+ + PhC2H5

10.10(M+ H)+ + CH4(M + H)+ + C2H4
(M + H)+ + C3H4
(M + C3H5)+(M + C3H5)+ = PhCH2+(M + C3H5)+ = C7H7+o-(M + H)+ + CH4m-(M + H)+ + CH4
p-(M + H)+ + CH4i-(M + H)+ + CH4(M + H)+(exp.) + CH4o-(M + H)+ + C2H4
m-(M + H)+ + C2H4
p-(M + H)+ + C2H4i-(M + H)+ + C2H4
(M + H)+(exp.) + C2H4o-(M + H)+ + C3H4
m-(M + H)+ + C3H4
p-(M + H)+ + C3H4i-(M + H)+ + C3H4
(M + H)+(exp.) + C3H4o-(M + C3H5)+m-(M + C3H5)+p-(M + C3H5)+i-(M + C3H5)+
o-CH3C6H4CH2+ + C2H4
m-CH3C6H4CH2+ + C2H4
p-CH3C6H4CH2+ + C2H4C7H6CH3+ + C2H4
PhCH2+ + C3H6
C7H7+ + C3H6o-(M + H)+ + CH4m-(M + H)+ + CH4
p-(M + H)+ + CH4i-(M + H)+ + CH4(M + H)+(exp.) + CH4(M + H - CH4)+=PhCH2+(M + H - CH4)+=C7H7+(M + H - C2H4)+=PhH2+o-(M + H)+ + C2H4
m-(M + H)+ + C2H4
p-(M + H)+ + C2H4i-(M + H)+ + C2H4
(M + H)+(exp.) + C2H4o-(M + H)+ + C3H4
m-(M + H)+ + C3H4
p-(M + H)+ + C3H4i-(M + H)+ + C3H4
(M + H)+(exp.) + C3H4o-(M + C3H5)+

8.07
9.39
10.61
9.89
9.87
9.34
9.17
9.29
9.11
9.60
8.69
9.17
9.29
9.11
9.60
8.69
10.61
10.73
10.54
11.04
10.13
9.29
9.43
9.24
9.82
9.92
9.95
9.80
9.63
9.53
9.01
7.67
7.80
7.59
8.04
7.08
7.78
7.26
8.62
8.98
9.11
8.91
9.35
8.39
10.42
10.55
10.34
10.79
9.83
9.09

-2.16
-0.82
-0.05
-0.77
-0.79
-1.32
-0.70
-0.58
-0.76
-0.27
-1.18
-0.70
-0.58
-0.76
-0.27
-1.18
0.29
0.41
0.22
0.72
-0.19
-1.03
-0.89
-1.08
-0.50
-0.40
-0.37
-0.52
-0.69
-0.79
-1.31
-2.00
-1.87
-2.08
-1.63
-2.59
-1.89
-2.41
-1.05
-0.67
-0.54
-0.74
-0.30
-1.26
0.32
0.45
0.24
0.69
-0.27
-1.01

Chemicalstructurec)
1
1
1
2
3
4
5a
5b
5c
5d
5
5a
5b
5c
5d
5
5a
5b
5c
5d
5
6a
6b
6c
6d
7a
7b
7c
8
9
10
11a
11b
11c
11d
11
12
13
14
11a
11b
11c
11d
11
11a
11b
11c
11d
11
15a

Ion-molecule reactions of RH+ with aromatic hydrocarbons

10

Table A1. Continued.

m-(M + C3H5)+p-(M + C3H5)+i-(M + C3H5)+o-C2H5C6H4CH2+ + C2H4
m-C2H5C6H4CH2+ + C2H4
p-C2H5C6H4CH2+ + C2H4

CH5+ + PhC2H3

10.90

C2H5+ + PhC2H3

10.88

C3H5+ + PhC2H3

11.33

CH5+ + PhC2H

12.53

C7H6C2H5+ + C2H4
PhCHCH3+ + C3H6C7H6CH3+ + C3H6
PhCHCH3+C7H6CH3+
PhCH2CH2+o-(M + H)+ + CH4m-(M + H)+ + CH4
p-(M + H)+ + CH4i-(M + H)+ + CH4(M + H)+(exp.) + CH4
PhCHCH3+ + C2H4C7H6CH3+ + C2H4
PhCH2CH2+ + C2H4o-(M + H)+ + C2H4
m-(M + H)+ + C2H4
p-(M + H)+ + C2H4i-(M + H)+ + C2H4
(M + H)+(exp.) + C2H4
PhCHCH2C2H5+
PhCH(C2H5)CH2+
o-(M + C2H5)+m-(M + C2H5)+p-(M + C2H5)+i-(M + C2H5)+
PhCH2+ + C3H6
C7H7+ + C3H6
PhCHCH3+ + C3H4C7H6CH3+ + C3H4
PhCH2CH2+ + C3H4o-(M + H)+ + C3H4
m-(M + H)+ + C3H4
p-(M + H)+ + C3H4i-(M + H)+ + C3H4
(M + H)+(exp.) + C3H4
PhCHCH2C3H5+
PhCH(C3H5)CH2+
o-(M + C3H5)+m-(M + C3H5)+p-(M + C3H5)+i-(M + C3H5)+o-C2H3C6H4CH2+ + C2H4
m-C2H3C6H4CH2+ + C2H4
p-C2H3C6H4CH2+ + C2H4C7H6C2H3+ + C2H4
PhCH2+ + C4H6
C7H7+ + C4H6
PhCHCH+ + CH4
PhCCH2+ + CH4

9.22
9.05
9.56
9.75
9.78
9.61
9.49
9.41
9.29
8.43
8.31
9.82
8.81
9.06
8.76
9.39
8.03
9.74
9.63
11.13
10.12
10.38
10.08
10.70
9.34
8.67
8.38
9.19
9.43
9.13
9.88
9.53
9.01
11.18
11.06
12.57
11.55
11.81
11.51
12.14
10.78
9.78
9.43
10.28
10.52
10.22
10.95
10.87
11.04
10.80
10.66
11.01
10.49
11.62
10.21

-0.88
-1.05
-0.54
-0.35
-0.32
-0.49
-0.61
-0.69
-0.81
-2.47
-2.59
-1.08
-2.09
-1.84
-2.14
-1.51
-2.87
-1.14
-1.25
0.25
-0.76
-0.50
-0.80
-0.18
-1.54
-2.21
-2.50
-1.69
-1.45
-1.75
-1.00
-1.35
-1.87
-0.15
-0.27
1.24
0.22
0.48
0.18
0.81
-0.55
-1.55
-1.90
-1.05
-0.81
-1.11
-0.38
-0.46
-0.29
-0.53
-0.67
-0.32
-0.84
-0.91
-2.32

15b
15c
15d
16a
16b
16c
17
18
19
20
21
22
23a
23b
23c
23d
23
20
21
22
23a
23b
23c
23d
23
24
25
26a
26b
26c
26d
27
28
20
21
22
23a
23b
23c
23d
23
29
30
31a
31b
31c
31d
32a
32b
32c
33
27
28
34
35

令和元年度

九州大学大学院総合理工学報告第 41 巻

第2号

11

Table A1. Continued.

o-(M + H)+ + CH4m-(M + H)+ + CH4
p-(M + H)+ + CH4i-(M + H)+ + CH4

10.45
-2.08
36a
10.65
-1.88
36b
10.42
-2.11
36c
11.01
-1.52
36d
(M + H)+(exp.) + CH4
9.59
-2.94
36
+
C2H5 + PhC2H
12.51
PhCHCH+ + C2H4
12.94
0.43
34
PhCCH2++ C2H4
11.52
-0.99
35
o-(M + H)+ + C2H4
11.77
-0.74
36a
m-(M + H)+ + C2H4
11.96
-0.55
36b
p-(M + H)+ + C2H4
11.73
-0.78
36c
i-(M + H)+ + C2H4
12.32
-0.19
36d
(M + H)+(exp.) + C2H4
10.91
-1.60
36
PhCCHC2H5+
10.34
-2.17
37
PhC(C2H5)CH+
11.84
-0.67
38
o-(M + C2H5)+
10.86
-1.65
39a
m-(M + C2H5)+
11.02
-1.49
39b
p-(M + C2H5)+
10.78
-1.73
39c
i-(M + C2H5)+
11.44
-1.07
39d
PhCH2+ + C3H4
11.30
-1.21
40
C7H7+ + C2H4
10.78
-1.73
41
C3H5+ + PhC2H
12.97
o-(M + H)+ + C3H4
13.20
0.23
1
m-(M + H)+ + C3H4
13.40
0.43
1
p-(M + H)+ + C3H4
13.17
0.20
1
i-(M + H)+ + C3H4
13.76
0.79
1
(M + H)+(exp.) + C3H4
12.34
-0.63
1
PhCHCH+ + C3H4
14.37
1.40
34
PhCCH2+ + C3H4
12.96
-0.01
35
PhCCHC3H5+
11.44
-1.53
42
PhC(C3H5)CH+
12.87
-0.10
43
o-(M + C3H5)+
11.95
-1.02
44a
m-(M + C3H5)+
12.11
-0.86
44b
p-(M + C3H5)+
11.87
-1.10
44c
i-(M + C3H5)+
12.51
-0.46
44d
naphthalene+ + CH3
11.21
-1.76
45
o-C2HC6H4CH2+ + C2H4
12.50
-0.47
46a
m-C2HC6H4CH2+ + C2H4
12.62
-0.35
46b
p-C2HC6H4CH2+ + C2H4
12.44
-0.53
46c
C7H6C2H+
12.26
-0.71
47
PhCH2+ + CH2CCCH2
12.92
-0.05
40
C7H7+ + CH2CCCH2
12.40
-0.57
41
PhCH2+ + CH2CHCCH
12.49
-0.48
40
C7H7+ + CH2CHCCH
11.97
-1.00
41
a) The symbols o-, m-, p-, and i- represent ortho-, meta-, para-, and ipso-adduct ions, respectively.
Thermochemical data calculated using reliable experimental values for ions in Ref. 11 areshown by exp., and the other values for ions are calculated using a PM3 method. b)
ΔH0(Reaction) = ΣΔH0(Product) – ΣΔH0(Reactant). (c) Chemical structures in Scheme 15.