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Explain the configuration and conformational aspect of disubstituted and trishna figured cyclohexane derivatives . How their chirality depend upon the nature of substitutent

Explain the configuration and conformational aspect of disubstituted and trishna figured cyclohexane derivatives . How their chirality depend upon the nature of substitutent
 

Grade:12th pass

1 Answers

jyoti bhatia
202 Points
5 years ago

What is the preferred conformation of cis-1,2-dichlorocyclohexane? 

The two guidelines we have for conformation of 6-rings are:

  • The carbon ring is in a chair.
  • Larger substituents are in equatorial positionsIt is important to realize that we cannot draw a conformation for cis-1,2-dichlorocyclohexane which easily fits the criteria we have used so far: a chair, with large groups equatorial. So what do we do? Clearly, the conformation of this compound must, in some way, involve more issues than what we have considered so farOne simple way to proceed is to re-examine the two criteria we have been using, and then state a generality about what to do in the event of a conflict. That generality is: use the chair, and then fit the groups as best you can. That is, try to put as many of the larger groups equatorial as you can, but realize that you may not get them all equatorial.It is cis compound if at each substituted position the Cl is "above" the H; that is, both Cl are on the same side of the ring.Second, this is a proper chair if adjacent axial groups point in opposite directions. The axial Cl on the upper right C should be "up", and the axial H on the lower right C must be "down". Thus, these aspects satisfy the proper way to orient things, in general, on a cyclohexane chair.Some compounds cannot be easily drawn within the common "rules". cis-1,2-dichlorocyclohexane is one such example. In this case, we kept the basic chair conformation, but put one larger group in the less favored axial orientation. Measurements on many such chemicals have shown that the energetic penalty of moving a cyclohexane ring much away from the basic chair conformation is quite large -- certainly larger than the energetic penalty of putting one "somewhat large" group in an axial position. With larger groups or more groups, this might not hold.

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