Steric dependence

The steric dependence is imposed by the bulky trimethylamine leaving group. In the TS for anti elimination, steric repulsion is increased as and increase in size. When the repulsion is sufficiently large, the TS for syn elimination is preferred. 

An alternative explanation of the experimental results is afforded by the assumption that the reaction involves the formation of an intermediate wherein the position of the double bond of the olefin is rendered indistinguishable. The observed rate of hydroformylation would then be the rate of formation of this intermediate. Owing to the great effect of steric factors on the rate of hydroformylation, one would expect that the rate of formation of this intermediate would be sterically dependent. Once formed, the intermediate reacts further to yield the aldehydes, the structures of which depend only on the intermediate and not on the reacting olefin. The exact nature of such an intermediate is unknown. 

The Tt-based hydrophobicity scale shows the side chain of aspartic acid, -CH2-COO , to be significantly less polar than that of glutamic acid, -CH2-CH2-COO . This is not as expected from the number of CH2 groups in the side chains and likely arises from steric-dependent hydrogen bonding interactions with nearby... 

In the HAM of internal olefins with rhodium Xantphos-type ligands, the same steric dependency on the bite angle concerning the formation of the linear amine as in hydroformylation was observed. An increase in the bite angle up to 125°, which was realized with Nixantphenoxaphos (1), resulted in an increase in n-regioselectivity, whereas with wider angles a reversed tendency was... 

Brown, H. C. Jadhav, P. K. Mandal, A. K. 1982. Hydroboration. 62. Monoisopinocampheylborane, an excellent chiral hydroborating agent for trans-disubstituted and trisubstituted alkenes. Evidence for a strong steric dependence in such asymmetric hydroborations. 7. Org. Chem. 47 5074-5083. 

Figure 6.4 Leading pairwise steric exchange interactions for methyl torsional variations in cis-NMF (cf. Fig. 6.3), showing locaUzed methyl

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