Cyclopropyl group effective size

The effective size of the cyclopropyl group is a matter of considerable importance. However, the quantitative measurement of the size of this group gave a very deceptive... 

Next, the effect on activity with respect to the size of the alkyl group in our series compared to that disclosed in the literature (2,4) was of interest. The effectiveness of alkyl groups is reported to be cyclopropyl > isopropyl > ethyl > methyl. In fact, this trend was followed in the [1,1 -biphenyl]-2-methyl-3-methanol derived alkyl aryl oxime ethers. This is illustrated with the (E,Z)-4-trifluoromethoxyphenyl(alkyl)methanone oxime ethers, Compounds 14, 16, 19 (Table V). The activity of this series increases with increasing size of the alkyl group. However, when cyclobutyl was incorporated, activity was lost. The cyclopropyl was the most effective while the isopropyl group was somewhat less effective. Other alkyl changes resulted in a rapid loss of activity. 

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