Preparation of alkanes

Question

What are the name of the compounds which are formed by the reaction of 2-bromopentane and 2-methyl 3-chlorobutane with sufficient amount of Na?

Answer 1

Hello Alexa

 

Listed below are 3 reactions that can occur resulting in the formation of 3 different alkane products.  I drew out the condensed structures for the 3 products (hopefully the formatting does not get distorted), but you may wish to re-draw them in a neater as well as a more readable form.

 

The structure of 2-bromopentane is:

 

        Br

         l

CH₃−CH−CH₂CH₂CH₃

 

The structure of 2-methyl-3-chlorobutane (FYI: the correct name for this compound should actually be 2-chloro-3-methylbutane since chloro gets a higher priority than methyl in IUPAC nomenclature.  However, the structure illustrated below is the same) is:

 

    H₃C    Cl
         l     l
CH₃−CH−CH−CH₃

 

 

REACTION #1: 2-Bromopentane + 2-methyl-3-chlorobutane

 

        Br                                  H₃C     Cl
         l                                        l      l
CH₃−CH−CH₂CH₂CH₃   +   CH₃−CH−CH−CH₃      →

 

   

              CH₃

               l

H₃C−CH−CH−CH₃

         l

CH₃−CH−CH₂CH₂CH₃

 

 

Longest carbon chain is 7 carbons, therefore, the alkane is heptane.  Carbons 2, 3 and 4 each have a methyl group bonded to them.  All together, there are three methyl groups (trimethyl).

 

Final name is:  2,3,4-Trimethylheptane

 

 

REACTION #2: 2-Bromopentane +  2-Bromopentane

 

        Br                                   Br
         l                                     l
CH₃−CH−CH₂CH₂CH₃  +  CH₃−CH−CH₂CH₂CH₃    →

 

 

H₃C−CH−CH₂CH₂CH₃

         l

CH₃−CH−CH₂CH₂CH₃

 

Longest carbon chain is 8 carbons, therefore, the alkane is octane. Carbons 4 and 5 each have a methyl group bonded to them. All together, there are two methyl groups (dimethyl).

Final name is: 4,5,-Dimethyloctane

 

 

REACTION #3: 2-Methyl-3-chlorobutane + 2-methyl-3-chlorobutane

 

      H₃C   Cl                      H₃C    Cl
          l     l                           l     l
CH₃−CH−CH−CH₃   +  CH₃−CH−CH−CH₃        →

 

 

            H₃C    CH₃

                l      l

    H₃C     CH−CH−CH₃ 

         l      l

CH₃−CH−CH−CH₃

 

 

Longest carbon chain is 6 carbons, therefore, the alkane is hexane. Carbons 2, 3, 4 and 5 each have a methyl group bonded to them. All together, there are four methyl groups (tetramethyl).

Final name is: 2,3,4,5,-Tetramethylhexane