Q4-41E - Organic Chemistry (Mcmurry)

Question

Assume that you have a variety of cyclohexane substituted in the positions indicated. Identify the substituents as either axial or equatorial. For example, a 1, 2-cis relationship means that one substituent must be axial and one equatorial, whereas a 1, 2-trans relationship means that either substituent is axial or both are equatorial.

 (a) 1, 3-Trans disubstituted                (b) 1, 4-Cis disubstituted

 (c) 1, 3-Cis disubstituted                    (d) 1, 5-Trans disubstituted 

 (e) 1, 5-Cis disubstituted                     (f) 1, 6-Trans disubstituted

Step-by-Step Solution

Answer

1. Both the substituents are either axial or equatorial.
2. One substituent is axial, and the other is equatorial.
3. One substituent is axial, and the other is equatorial.
4. Both the substituents are either axial or equatorial.
5. One substituent is axial, and the other is equatorial.
6. Both the substituents are either axial or equatorial.

Step 1: Chair form of cyclohexane

There are four conformations possible for cyclohexane such as a chair, twist boat, boat, half chair. Among all the four conformations chair form of cyclohexane is considered a very stable one. Chair conformation of cyclohexane is as follows;

Chair form of cyclohexane

We simply can say if the relation is up-up then cis, if down–down relationship then trans.

If the up-down or down-up relation between the bond then trans.

Step 2: Axial or equatorial position of above substituents

a.     1,3-trans disubstituted cyclohexane.

        Both the substituents are either axial or equatorial.

b.  

          cis-1,4-disubstituted cyclohexane

          One substituent is on axial, while another one is on equatorial position.

c.

         1,3-cis disubstituted cyclohexane

          One substituent is axial, and the other is equatorial.

d.

      

     1,5-trans disubstituted cyclohexane

     Both the substituents are either axial or equatorial.

e.

        1,5-cis disubstitued cyclohexane

         One substituent is axial, and the other is equatorial.

f.

          1,6-trans disubstitued cyclohexane

           Both the substituents are either axial or equatorial.