(a) When n-heptane burns in a gasoline engine, the combustion process takes place to...

(a) When n-heptane burns in a gasoline engine, the combustion process takes place too quickly.The explosive detonation makes a noise called knocking. When 2,2,4-trimethylpentane(isooctane) is burned, combustion takes place in a slower, more controlled manner.Combustion is a free-radical chain reaction, and its rate depends on the reactivity ofthe free-radical intermediates. Explain why isooctane has less tendency to knock thandoes n-heptane.

(b) Alkoxy radicals are generally more stable than alkyl radicals. Write anequation showing an alkyl free radical (from burning gasoline) abstracting a hydrogenatom from tert-butyl alcohol, (CH₃)COH. Explain why tert-butyl alcohol works as anantiknock additive for gasoline.

(c) Use the information in Table 4-2 (page 143) to explain why toluene (PhCH₃) has a veryhigh octane rating of 111. Write an equation to show how toluene reacts with an alkylfree radical to give a relatively stable radical.