Steric strain diaxial interaction

Diaxial interaction Transannular strain due to steric crowding of axial substituents across a ring. Diazo compound A diazoalkane, R2C=N2, such as diazomethane (CH2N2), a useful synthetic... 

The energy difference between axial and equatorial conformations is due to steric strain caused by 1,3-diaxial interactions. The axial methyl group on Cl is too close to the axial hydrogens three carbons away on C3 and C5, resulting in 7.6 kj/mol of steric strain (Figure 4.13). 

Figure 4.14 The origin of 1,3-diaxial interactions in methylcyclohexane. The steric strain between an axial methyl group and an axial hydrogen atom three carbons away is identical to the steric strain in gauche butane. Note that the -CH3 group in methylcyclohexane moves slightly away from a true axial position to minimize the strain.

Chair cyclohexanes are conformationally mobile and can undergo a ring-flip, which interconverts axial and equatorial positions. Substituents on the ring are more stable in the equatorial position because axial substituents cause 1,3-diaxial interactions. The amount of 1,3-diaxial steric strain caused by an axial substituent depends on its hulk. 

Diaxial interaction (Section 4.8) The strain energy caused by a steric interaction between axial groups three carbon atoms apart in chair cyclohexane. 

When all 12 substituents are hydrogen atoms, there is no steric strain. The presence of any groups larger than H changes the stability by increasing the steric strain, especially if these groups are present in axial positions. When axial, diaxial interaction can cause steric strain. In the equatorial case, there is more room and less steric strain. Bulky groups always preferably occupy equatorial positions. 

The energy difference bet ween axial and equatorial confbrmer.5 is due to sterk strain caused by so-called 1,3-diaxial interactions. That iSt the axial methyl graup on Cl ia too close to the axial hydroftens three carbons aivay oit Cl and C, resulting in 7.6 W/mol of steric strain i Figure 4.201. 

Approximately how much steric strain does the 1,3-diaxial interaction between the two methyl groups introduce into the diaxial conformation of cis-l,3-dimethylcyclo-hexane (See Problem 4.44.)... 

Ireland s deprotonation model is widely used to rationalize the stereochemistry with various ethyl ketones and bases. " In the absence of additives that solvate the lithium cation such as HMPA, proton transfer occurs via a chair-hke closed transition state. Under these conditions, the (Z)-enolate is disfavored because of the 1,3-diaxial interaction between the Me and the i-Pr group on nitrogen. As the steric requirement of the R group increases, so does the A strain between the R and Me groups in forming the double bond, thus destabilizing the ( )-(0)- relative to the (Z)-(0)-enolate (Table 6.2). 

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