Q48E - Organic Chemistry (Mcmurry)

Question

The relative rate of radical bromination is 1; 82; 1640 for 1°;2°;3°

hydrogens, respectively. Draw all of the monobrominated products that

you might obtain from the radical bromination of the compounds

below. Calculate the relative percentage of each.

(a) Methylcyclobutane

(b) 3,3-dimethylpentane

(c) 3-methylpentane

Step-by-Step Solution

Answer

1. Relative percentage of primary C-H = 0.15%

           Relative percentage of primary C-H = 23.1%

           Relative percentage of primary C-H = 76.8%

 

         2.Relative percentage of primary C-H = 3.6%

           Relative percentage of primary C-H = 96.4%

            Relative percentage of primary C-H = 0%

 

       3.Relative percentage of primary C-H = 0.45%

           Relative percentage of primary C-H = 16.59%

            Relative percentage of primary C-H = 82.9%

Step-by-step Solution Step 1: Bromination

Bromination is a chemical reaction involving the reaction of a compound and bromine results in bromine being added to the compound.

Step 2: Calculate relative percentage and sketch monobrominated product

Mono bromination of cyclobutane results in four products

Methyl cyclobutane has three equivalent primary C-H, six equivalent secondary C-H and one tertiary C-H.

The ratio of primary C-H =3 × 1= 3            

The ratio of secondary C-H = 6 × 82 = 492

The ratio of tertiary C-H =1 ×1640 = 1640

Total ratio = (3+492+1640) = 2135

(a)  Relative percentage of primary C-H $=\frac{3}{2135}\times 100=0.15\%$

 

    Relative percentage of primary C-H  $=\frac{492}{2135}\times 100=23.1\%$

 

     Relative percentage of primary C-H $=\frac{1640}{2135}\times 100=76.8\%$

Mono bromination of cyclobutane

(b)

Mono bromination of 3,3-dimethylpentane results in four products

Methyl cyclobutane has three equivalent primary C-H, six equivalent secondary C-H and one tertiary C-H.

The ratio of primary C-H =3 × 12= 36

The ratio of secondary C-H = 12 × 82 = 984

The ratio of tertiary C-H =0×1640 = 0

Total ratio = (36+984+0) = 1020

(a) Relative percentage of primary C-H $=\frac{36}{984}\times 100=3.6{\%}_{}^{}$

 

    Relative percentage of primary C-H  $=\frac{984}{1020}\times 100=96.4\%$

 

    Relative percentage of primary C-H = $=\frac{0}{1020}\times 100=0\%$

Mono bromination of3,3-dimethylpentane

(c)

Mono bromination of3-methylpentane results in four products

Methyl cyclobutane has nine equivalent primary C-H, four equivalent secondary C-H and one tertiary C-H.

The ratio of primary C-H =9× 1= 9

The ratio of secondary C-H = 4× 82 = 328

The ratio of tertiary C-H =1 ×1640 = 1640

Total ratio = (9+328+1640) = 1977

(a) Relative percentage of primary C-H  $=\frac{9}{1977}\times 100=0.45\%$

 

     Relative percentage of primary C-H  $=\frac{328}{1977}\times 100=16.59\%$

 

     Relative percentage of primary C-H $=\frac{1640}{1977}\times 100=82.9\%$

Mono bromination of 3-methylpentane