Pyramidal Carbocations

Abstract

Dedicated to Professor Ferdinand Bohlmann on the occasion of his 60th birthday Pyramidal cations are discussed with reference to their role as the connecting link between organic and inorganic chemistry. The electronic structure of these ions is treated with respect to their physical and chemical properties, namely charge distribution, geometry, and quenching reactions with nucleophiles. The chemistry in the gas phase of certain carbenium ions, in particular the scrambling of carbon atoms, is readily explicable by invoking transition states or intermediates of pyramidal structure. Moreover, the behavior of unimolecular processes can be understood in terms of transition states in which a hydrogen molecule is positioned as a "side-on" or an "end-on" ligand. Volume 20 -Number 12 December 1981 Pages 991 -1 066 Angew. Chem. Inr. Ed. Engl. 20. 991-1003 (1981) 0 Verlag Chemie GmbH. 6940 Weinheim, 1981 0570-0833/81/1212-0991 $02.50/0 ( 73) Nu ( 74) NU I \ I I D Scheme 7. Quenching of pyramidal cations by nucleophiles Nue. Angew. Chem. Int. Ed. Engl. 20. 991-1003 (198I) Received: July 8, 1981 [Z 390 IE] German version: Angew. Chem. 93, 1046 (1981) 11) a) H. Hogeueen. P. W. Kwant. Acc. Chem. Res. 8, 413 (1975); b) H. C. Brown (with comments by P. uon R. Schleyer): The Nonclassical Ion Problem, Plenum Press, New York 1977, Chap. 1, p. 17.121 a) R. N. Grimes: Carboranes, Academic Press, New York 1970; b) W. N .

Helium Tagging Infrared Photodissociation Spectroscopy of Reactive Ions

“…The original case study for our instrument was the investigation of the benzene dication structure. , The benzene dication may be considered as a prototypical member of the nonclassical carbocation family. − The permethylated analog of C 6 H 6 2+ , C 6 (CH 3 ) 6 2+ , can be prepared in Magic acid solution from various precursors, and it has been shown to possess a pyramidal structure with a five-membered base and one carbon at the apex . It was found that vertical double ionization of benzene primarily yields dications with six-membered rings ( 3 1 2+ and 1 1 2+ , Scheme ), but theoretically, it was predicted that C 6 H 6 2+ should also adopt the pyramidal structure ( 1 2 2+ ). − …”

Identification of Active Sites and Structural Characterization of Reactive Ionic Intermediates by Cryogenic Ion Trap Vibrational Spectroscopy

“…For example, they include someo ft he "controversial" carbocations like the non-classical protonated methane [CH 5 ] + , [18,41,43] [44f] or the Jahn-Teller distorted adamantane radicalc ation [C 10 H 16 ]C + , [44f] not to speak of the spectacular laboratory confirmationo f[ C 60 ]C + as the carriero ft wo diffuse interstellar bands, [45] or the structural characterization of [C 6 H 6 ] 2 + isomersi ncluding the celebrated pyramidal [C 6 H 6 ] 2 + with a C 5 H 5 base and CH group at the apex. [46] Similarly,t he structures of ions generated upon gas-phase protonation of the elusive sulfurous and carbonic acids [47] were identified by their IR signatures. [48] The early developmento fc ryogenic ion trap vibrational spectroscopy was directlyl inked with the characterizationo f metal oxide clusters, [20,24,26,37,49] which continuest oa ttract considerable interesti nt he context of identifying model systems for heterogeneous catalysis.…”

C5H4: Pyramidane and Its Low-Lying Isomers

“…Following the prediction of a stable pyramidal structure for the (CH) 5 + ion by Stohrer and Hoffman, experimental evidence ,, and theoretical results ,− for pyramidal bonding environments were presented by several researchers. Minkin and Schwarz have provided reviews of this subject.…”