Question

Explain why (CH3)2CHCH(Br)CH2CH3 reacts faster than (CH3)2CHCH2CH(Br)CH3 in an E2 reaction, even though both alkyl halides are 2°. The first structure has more hydrogens attached to the β carbons than the second structure. The major and minor products formed from the first structure have more alkyl groups on the C═C than those formed from the second structure. The major and minor products formed from the second structure have more alkyl groups on the C═C than those formed from the first structure. The second structure has more hydrogens attached to the β carbons than the first structure.

Answer 1

Answer:

The major and minor products formed from the first structure have more alkyl groups on the C═C than those formed from the second structure.

The second structure has more hydrogens attached to the β carbons than the first structure.

Explanation:

It is possible to explain the reaction based on Zaitsev’s rule that states that an elimination will normally lead to the most stable alkene as the major product.  This normally translates to it giving the most substituted alkene.

The two adjacent carbons in the first molecule are secondary. That means the two products will produce a disubstituted alkene but in the second molecule just one product will be disubstituted. Thus:

The first structure has more hydrogens attached to the β carbons than the second structure. FALSE. If the structure has more hydrogens will produce an alkene less stable.

The major and minor products formed from the first structure have more alkyl groups on the C═C than those formed from the second structure. TRUE. As the first structure have more alkyl groups the product is most stable.

The major and minor products formed from the second structure have more alkyl groups on the C═C than those formed from the first structure. FALSE. Is the opposite of the last option.

The second structure has more hydrogens attached to the β carbons than the first structure. TRUE. As the second structure has more hydrogens, the alkenes produced will be less substituted being less stable.

I hope it helps!