What are the major products for reaction with cis-1-chloro-3-methylcyclopentane and trans-1-chloro-3-methylcyclopentane with #"OH"^(-)# in water at high temperature?

Question

Maya Allen · Accepted Answer

The cis isomer will form 3- and 4-methylcyclopentene in roughly equal amounts. The trans isomer will form 4-methylcyclopentene as the major product.

What type of reaction?

I predict an #"E2"# elimination because:

The substrate is a secondary alkyl halide.
The substrate has at least one β-hydrogen: possible elimination.
The nucleophile (#"OH"^"-"#) is a strong base: possible elimination.
There is (presumably) a high base concentration: favouring #"E2"#.
Water is a polar protic solvent: favouring elimination.
The high temperature favours elimination.
cis-1-Chloro-3-methylcyclopentane

The structure of the substrate is

Elimination requires a trans arrangement of the β-hydrogen and the leaving group.

We see appropriate β-hydrogens at #"C2"# and #"C5"#.

Elimination of the hydrogen from #"C2"# forms 3-methylcyclopentene.

Elimination of the hydrogen from #"C5"# forms 4-methylcyclopentene.

These two isomers would probably be formed in roughly equal amounts.

trans-1-Chloro-3-methylcyclopentane

The structure of the substrate is

Again, we see trans β-hydrogens at #"C2"# and #"C5"#.

However, elimination will be slower in each case because of steric hindrance by the methyl group.

Elimination of the hydrogen from #"C5"# will be faster than from #"C2"# because of its greater distance from the methyl group.

Thus, the major product will be 4-methylcyclopentene.

Paisley Boney · Answer

undefined The major products for the reaction of cis-1-chloro-3-methylcyclopentane and trans-1-chloro-3-methylcyclopentane with OH^- in water at high temperature are 3-methylcyclopentan-1-ol and HCl.