Question

Arrange the following alkenes in order of their decreasing heat of combustion values:

• A. $1>2>3$
• B. $1>3>2$
• C. $2>3>1$
• D. $3>2>1$

Answer 1

The correct option is B $1>3>2$


Alkene 1 has 2 alpha hydrogens.
Alkene 2 has 8 alpha hydrogens.
Alkene 3 has 6 alpha hydrogens.
More the number of alpha hydrogens more is the stability and lesser is the heat of combustion.
Order of stability:
$2>3>1$
Decreasing order of heat of combustion:
$1>3>2$
So, (b) is the correct option.