Cyclobutanes cyclopropanes

TABLE 10. Conventional strain energies (CSE), hybridizations, s-character, overlap values, overlap repulsions and geminal delocalizations of propane, cyclobutane, cyclopropane and their heterologues with X = NH, O, SiH2, PH, S from Reference 47 ... 

Compare the boiling points of cyclopentane and cyclobutane. Use this information to put the following compounds in order from highest to lowest boiling point cyclohexane, cyclobutane, cyclopropane, cyclopentane. 

Since the pioneering observation of Demjanov that both cyclobutylamine and cyclopropylcarbinylamine react with nitrous acid to give a mixture of cyclobutanol and cyclopropylcarbinoP , the facile interconversions which occur among related cyclobutane, cyclopropane and open-chain structures via carbenium ion intermediates have been extensively studied. This question has been discussed in Section III.A for a review concerning the formation, structure and ring contraction of cyclobutyl cations, see Ref. 264. 

The cationic rearrangement of cyclobutyl compounds to cyclopropylmethyl derivatives is a well-studied reaction which, like the homoallylic rearrangement, has been mainly investigated in connection with the fate and nature of the cyclobutyl cation.Again the synthetic value of this rearrangement is limited because generally mixtures of cyclobutanes, cyclopropanes and alkenes are obtained. 

Among the many interconversions which occur readily in related cyclobutane, cyclopropane and open-chain frameworks, the stereospecific rearrangement of a-halo- or a-tosyloxycy-clobutanones into cyclopropanecarboxylic acid derivatives, has been shown to follow the semi-benzilic rearrangement mechanism, i. e. addition of nucleophiles to the carbonyl carbon atom and concerted displacement of halide (or tosyloxy) ions with 1,2-migration of the Ca — C carbonyl bond (see Section 4.1.2.2.5.). °... 

Cyclopentane, cyclobutane, cyclopropane, and many other cyclic molecules have been studied, hi the fundamental region, the frequency increases as the ring becomes more strained, and the first overtones reflect this trend. Cyclopentane s two strongest first overtone peaks are at 5730 cm (1745 nm) and 5834 cm (1714 nm) for example, as compared to cyclohexane s 5697 and 5791 cm . ... 

As final examples, the intramolecular cyclopropane formation from cycloolefins with diazo groups (S.D. Burke, 1979), intramolecular cyclobutane formation by photochemical cycloaddition (p. 78, 297f., section 4.9), and intramolecular Diels-Alder reactions (p. 153f, 335ff.) are mentioned. The application of these three cycloaddition reactions has led to an enormous variety of exotic polycycles (E.J. Corey, 1967A). 

Cyclobutane has less angle strain than cyclopropane and can reduce the torsional strain that goes with a planar geometry by adopting the nonplanar puckered confer matron shown m Figure 3 11... 

Cyclopropane is planar and destabilized by angle strain and torsional strain Cyclobutane is nonplanar and less strained than cyclopropane... 

Cyclobutane has less angle strain than cyclopropane (only 19.5°). It is also believed to have some bent-bond character associated with the carbon-carbon bonds. The molecule exists in a nonplanar conformation in order to minimize hydrogen-hydrogen eclipsing strain. 

Chiral Alcohols and Lactones. HLAT) has been widely used for stereoselective oxidations of a variety of prochiral diols to lactones on a preparative scale. In most cases pro-(3) hydroxyl is oxidized irrespective of the substituents. The method is apphcable among others to tit-1,2-bis(hydroxymethyl) derivatives of cyclopropane, cyclobutane, cyclohexane, and cyclohexene. Resulting y-lactones are isolated in 68—90% yields and of 100% (164,165). 

C-C bond Fluonnation increases the bond strengths in cycloalkanes, including cyclobutanes [75, 94], but by contrast, it decreases C-C bond strengths and increases nng strain in cyclopropanes and other three-membered nng compounds [75 94. 9S]... 

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