In:
Israel Journal of Chemistry, Wiley, Vol. 20, No. 1-2 ( 1980-01), p. 43-50
Abstract:
The structures (4‐31G optimization) and energies (6‐31G*) of vinyl lithium ( 5 ) and of the 1,1 ( 3 and 4 ), cis ‐1,2 ( 6 ), trans ‐1,2 ( 7 ) and doubly bridged ( 8 ) dilithioethylenes have been calculated using standard ab initio methods. Vinyl lithium ( 5 ), indicated to have a classical geometry, is about 11 kcal/mole more stable than ethyl lithium in an hydride exhange reaction (Eq. (2)). Singlet trans ‐1,2‐dilithioethylene, the most stable C 2 H 2 Li 2 isomer (see also addendum), has a highly distorted, partially bridged structure ( 7a ) with 〈 CCLi = 87°. Symmetrically bridged 8 and the cis ‐isomer 6 are considerably less stable, 54 and 19 kcal/mole, respectively. The partial Li‐H bonding in 7a contributes significantly to this behavior. 1,1‐Dilithioethylene is found to prefer a perpendicular ( 3 ) over the usual planar ( 4 ) geometry both in singlet and in triplet states. Triplet symmetrically bridged 8 and triplet cis dilithioethylene ( 6 ) are indicated to be local minima, but are less stable than singlet trans 7a . Cis ‐dilithioethylene ( 6 ) is indicated to be thermodynamically unstable towards dissociation into Li 2 and acetylene. This factor, and the low lying triplet state, may contribute to the experimental difficulties in preparing 6 . The nature of the carbon–lithium bonding in these molecules is discussed. We find that an electrostatic model cannot account for the structural details or for the relative energies of the C 2 H 2 Li 2 isomers. The importance of the multicenter covalent nature of bonding to lithium is emphasized.
Type of Medium:
Online Resource
ISSN:
0021-2148
,
1869-5868
DOI:
10.1002/ijch.v20:1-2
DOI:
10.1002/ijch.198000051
Language:
English
Publisher:
Wiley
Publication Date:
1980
detail.hit.zdb_id:
2066481-3
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