Single Choice

Rank the following alkenes in order of decreasing heats of hydrogenation: (largest first)

A$$2 > 3 4 > 1$$
B$$2 > 4 > 3 > 1$$
C$$1 > 3 > 4 > 2$$
D$$1 > 4 > 3 > 2$$
Correct Answer

Solution

More stable the alkene, less is the heat of hydrogenation. Among the given alkene, $$2$$ is most stable as it is stabilized through hyperconjugation by $$8$$ alpha-hydrogens. In case of $$3$$ and $$4$$, the number of alpha hydrogen $$6$$, whereas for $$1$$ has the least alpha hydrogen equal to $$2$$. Hence heat of hydrogenation will be maximum for $$1$$.
Between $$3$$ and $$4$$, $$4$$ will have higher heat as it has a net dipole moment whereas $$4$$ has zero dipole moment.
Hence, the required order is- $$1>4>3>2$$

SIMILAR QUESTIONS

Hydrocarbons

Ethylene is converted to ethane in the presence of $$Ni$$ at $$300^{0}C$$ . In this reaction the hybridization of carbon changes from :

Hydrocarbons

A hydrocarbon $$'X'$$ adds on one mole of hydrogen to give another hydrocarbon and decolourised bromine water. $$'X'$$ reacts with $${ KMnO }_{ 4 }$$ in the presence of acid to give two moles of the same carboxylic acid. The structure of $$'X'$$ is:

Hydrocarbons

Hydrogenation of $$C_{6}H_{5}CHOHCOOH$$ over $$Rh -Al_{2}O_{3}$$ gives :

Hydrocarbons

Compound(s) that on hydrogenation produce(s) optically inactive compound(s) is(are):

Hydrocarbons

Which one of the following alkenes will react faster with $$H_2$$ under catalytic hydrogenation conditions?

Hydrocarbons

Write structures of all the alkenes which on hydrogenation give 2 - methylbutane.

Hydrocarbons

Give the formula and name of $$A, B, C$$ and $$D$$ in the following equations: $$C_2H_2 \xrightarrow {H_2}\ A \xrightarrow{H_2}\ B\ \underset{-HBr}{\xrightarrow {Br_2}}\ C\ \underset{-HBr}{\xrightarrow {Br_2}}\ D$$

Hydrocarbons

Addition reaction and substitution reaction are type of organic reactions. Which type of reaction is shown by ethene?

Hydrocarbons

Which one of the following alkenes will react faster with $$H_2$$ under catalytic hydrogenation conditions?

Hydrocarbons

In which case the reaction is most exothermic with $$H_2$$ Ni.

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