Question

The general formula for alcohol is:

• A. C_nH_2n+2OH
• B. C_nH_2n+1OH
• C. C_nH_2n–1OH
• D. C_nH_2n+4OH

Answer 1

Answer: (B), (C)

The correct options are
B

C_nH_2n+1OH

C

C_nH_2n–1OH

The general formula of an alkane is $C_n{H}_{2n+2}$. A $-OH$ group replaces one of the hydrogens so the number of hydrogens and (-OH) is 2n+1 and 1. I.e. $C_n{H}_{2n+1}OH$ is one of the general formulae.

Options A and D have 2n+2 and 2n+4 hydrogens which are more than 2n+2 (an alkyne can have). I.e. such compounds do not exist.

The general formula of an alkene is $C_n{H}_{2n}$. A $-OH$ group replaces one of the hydrogens so the number of hydrogens and (-OH) is 2n-1 and 1. I.e. $C_n{H}_{2n-1}OH$ is also a possibility of the general formulae.