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Cyclopropane more acidic than cyclohexane. Give reason?

 Cyclopropane more acidic than cyclohexane. Give reason?
 
 

Grade:12th pass

3 Answers

Rajkamal Singh
15 Points
6 years ago
This is due to the angle strain in cyclopropane. It contains  sp3 hybridized  carbon whose angle should be 109.5 but in these case it is actually 60angle so it is acidic whereas in cyclohexane it non planer structure and stablised.
 
Arun
25750 Points
6 years ago
rings larger than 4 carbons have 3 dimensional shapes that relieve this bond strain, but it's important to note that bond strain does affect stability. For cyclopropane and cyclobutane, the strain energy is about 110 kj/mol. Cyclopentane, which is non-planar can remove some of the strain and has only about 25 kj/mol of strain. Hexane, because of its boat conformation, can maintain perfect tetrahedral angles, resulting in no strain. As the ring sizes go up, some angle strain is introduced again because rings are unable to achieve perfect tetrahedral angles, but the highest is about 9 members where the strain is only about 50 kj/mol. Ring strain pervades rings up to 13 members. After that, there are enough carbons that ring strain is removed completely. But angle strain isn't the only issue involved in ring strain. Torsional strain is also a factor. When the hydrogen bonds in a ring eclipse each other, this creates additional strain. In the cases of both cyclopropane and cyclobutane, again, because they're planar, their hydrogens eclipse each other, greatly adding to the strain. In fact, this is the cause of most of the strain found in cyclopentane. Cyclopentane has bond angles very close to 109.5°, but because 4 of its carbons are planar, there it has torsional strain that makes it less stable. Looking at the cyclopentane along 2 of the bonds on the plane, with the non-planar carbon closest to us, in the figure above, one can see that the bend in the bonds allows the hydrogens to move slightly out eclipse, reducing the torsional strain somewhat. 

Cyclohexane is the lowest membered ring that's able to have both 109.5° bond angles and maintain a staggered conformation, allowing it to be strain free.
Upendra Yadav
33 Points
6 years ago
This is due to the angle strain in cyclopropane. It contains  sp3 hybridized  carbon whose angle should be 109.5 but in these case it is actually 60angle so it is acidic whereas in cyclohexane it non planer structure and stablised.

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