Select from:
A). underwater;
B). at high altitudes;
C). in cold climates;
D). under extreme conditions;
Given those answer options, answer the question: Answer the following question given this paragraph: Because alkanes contain only CC and CH bonds, which are strong and not very polar (the electronegativities of C and H are similar; Figure 7.15 "Pauling Electronegativity Values of the "), they are not easily attacked by nucleophiles or electrophiles. Consequently, their reactivity is limited, and often their reactions occur only under extreme conditions. For example, catalytic cracking can be used to convert straight-chain alkanes to highly branched alkanes, which are better fuels for internal combustion engines. Catalytic cracking is one example of a pyrolysis reaction (from the Greek pyros, meaning "fire," and lysis, meaning "loosening"), in which alkanes are heated to a sufficiently high temperature to induce cleavage of the weakest bonds: the CC single bonds. The result is a mixture of radicals derived from essentially random cleavage of the various CC bonds in the chain. Pyrolysis of n-pentane, for example, is nonspecific and can produce these four radicals: Equation 24.7. Q: When do alkane reactions usually occur? A:
A:
D).