Strained hydrocarbon structures steric strain

Centropolyindanes constitute a complete family of arylaliphatic polycyclic hydrocarbons containing several indane units. Mutual fusion of the five-membered rings leads to three-dimensional, carbon-rich molecular frameworks bearing a central carbon atom, such as benzo-annelated [3.3.3]propellanes, triquinacenes, and [5.5.5.6]- and [5.5.5.5]fenestranes. In this review, the structural concept of centropolyindanes is contrasted to other fused indane hydrocarbons. Besides the syntheses of the parent centropolyindanes and recently described related indane hydrocarbons, the preparation of a large variety of bridgehead and arene substituted centropolyindanes is presented including strained, heterocyclic, and centrohexacyclic derivatives. In appropriate cases, the particular reactivity and some structural features of these unusual, sterically rigid polycyclic compounds are pointed out. 

The cation possesses a more favourable geometry than 1,6-methano-[10]annulene, being able to incorporate the 10 -system into a more planar structure. It is evidently more stable than the tropylium ion, as it can be formed from its neutral hydrocarbon precursor 57 by a hydride-transfer reaction with tropylium tetrafluoroborate 136>. The anion, on the other hand, involves substantial steric strain and is not as planar as either the cation or the neutral bridged [lOJannulene. Whereas formation of the cation from 57 was seen to be most favourable, the anion precursor 58 is much less acidic than cyclopentadiene, although in the presence of... 

The Jcc and Jcc couplings of allene and two sterically strained hydrocarbons, cyclopropane and cyclopropene, have been calculated by Ruden et at different levels of electronic-structure theory and compared with each other and with the experimental equilibrium constants obtained from experiment by subtracting the calculated vibrational contributions. 

Potential energy calculations have been employed in a description of the dynamic structure of adamantane and the nature of the order-disorder phase transition, as well as the mechanism of self-diffusion in the molecular solid. Theoretical calculations on the acid-catalysed hydrolysis of aliphatic esters lend support to the use of Taft , values as a measure of steric effects of alkyl groups correlation of with relative rate data (log k,., ) is discussed as well as that with steric energy parameters (from force-field calculations), which are found to parallel AAH values. " The same authors have outlined a new source of data of use in the estimations of van der Waals strain in hydrocarbons (including norbornane and adamantane). 

The [2]naphthaleno[2]paracyclophanes (430) and (431) have been synthesized with a view to observing strain and deformation of the naphthalene unit. [2.2.2](l,2,4)(l,3,5)Cyclophane (432) was made for examination of its strained and skew structure, and the novel triply clamped biphenylophane hydrocarbons (433) and (434) have been prepared for similar steric purposes. ... 

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