Cyclobutane, angle strain molecular model

The molecular models made for Exercise 4-1 reveal obvious differences between cyclopropane, cyclobutane, cyclopentane, and so forth, and the corresponding straight-chain alkanes. One notable feature of the first two members in the series is how difficult it is to close the ring without breaking the plastic tubes used to represent bonds. This problem is called ring strain. The reason for it lies in the tetrahedral carbon model. The C-C-C bond angles in, for example, cyclopropane (60°) and cyclobutane (90°) differ considerably from the tetrahedral value of 109.5°. As the ring size increases, strain diminishes. Thus, cyclohexane can be assembled without distortion or strain. 

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