Factors to Stabilize Hypervalent Bonds

TBP are four-coordinated, whereas MC are three. Therefore, the bulkiness around E will be more severe for TBP than for MC. The increased bulkiness around E prefers MC to TBP. Namely, it is possible to prepare hypervalent chalcogen compounds other than those predicted from the general rule based on X, by modulating electronic and/or steric conditions around chalcogens in organic chalcogen compounds. 

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