Which compound would you expect to have the largest heat of hydrogenation: 3,4-dimethyl-2-hexene, 2,3-dimethyl-2-hexene, or 4,5-dimethyl-2-hexene?

Answer 1

4,5-Dimethylhex-2-ene will have the largest heat of hydrogenation.

There are two principles to consider:

  • The least stable alkene will have the least highly substituted double bond.
  • The least stable alkene will have the highest heat of hydrogenation.

    The order of stability is

    monosubstituted < disubstituted < trisubstituted < tetrasubstituted

    The formula of 3,4-dimethylhex-2-ene is CH₃CH=C(CH₃)CH(CH₃)CH₂CH₃. This is a trisubstituted alkene.

    The formula of 2,3-dimethylhex-2-ene is (CH₃)₂C=C(CH₃)CH₂CH₂CH₃. This is a tetrasubstituted alkene.

    The formula of 4,5-dimethylhex-2-ene is CH₃CH=CHCH(CH₃)CH(CH₃)₂. This is a disubstituted alkene.

    4,5-Dimethylhex-2-ene is the least substituted alkene, so it is the least stable and gives the highest heat of hydrogenation.

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Answer 2

The compound that would be expected to have the largest heat of hydrogenation is 2,3-dimethyl-2-hexene.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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