Cyclobutane skeletal structure

The variety of methods for accomplishing the [2 + 2] cycloaddition and the reliability of this reaction secures its position as one of the most versatile tools for the creation of the cyclobutane fragment in a variety of structures. Additional attractive dimensions to the scope of this protocol come in the ease of further transformations through ring opening and skeletal rearrangements, typical for cyclobutane fragments " (this aspect will be considered later in this chapter). 

C=C—C—C—C—C. Isomerization to a methylpentane would result in localizing the carbonium ion on the tertiary position. This structure can no longer ring close to a cyclopentane but only to a highly strained cyclobutane. Since skeletal isomerization occurs readily at reforming conditions, most of the n-hexane would be converted to isohexane or cracked products rather than to cyclopentane. 

The name of a cycloalkane reveals the number of carbon atoms in the ring. For example, cyclopropane (CjHg) is the smallest cycloalkane, with three carbon atoms in the ring. Cyclobutane (C4Hg) has a ring with four carbon atoms. A cyclic hydrocarbon can be represented by condensed, skeletal, and line structures. These structures are illustrated below for cyclobutane. Chemists usually use line structures to depict cycloalkanes. 

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