Question

How many constitutional isomers in C4H8ClF?

Answer 1

I count 12 constitutional isomers of `"C"_4"H"_8"ClF"`.

Explanation:

I. Based on butane skeleton

(a) `"Cl"` on a terminal carbon

Four isomers:

• 1-chloro-1-fluorobutane
• 1-chloro-2-fluorobutane
• 1-chloro-3-fluorobutane
• 1-chloro-3-fluorobutane

(b) `"Cl"` on an internal carbon

Four isomers:

• 2-chloro-1-fluorobutane
• 2-chloro-2-fluorobutane
• 2-chloro-3-fluorobutane
• 3-chloro-1-fluorobutane

II. Based on 2-methylpropane

(a) `"Cl"` on a terminal carbon

Three isomers:

• 1-chloro-1-fluoro-2-methylpropane
• 1-chloro-2-fluoro-2-methylpropane
• 1-chloro-3-fluoro-2-methylpropane

(b) `"Cl"` on `"C2"`

One isomer:

• 2-chloro-1-fluoro-2-methylpropane

"We leave it as an exercise for the student" to draw the structural formulas of the isomers.