In:
Zeitschrift für Naturforschung B, Walter de Gruyter GmbH, Vol. 69, No. 11-12 ( 2014-12-1), p. 1384-1394
Abstract:
1,3,4,5-Tetraisopropyl-2-thioimidazoline (6b) was prepared by condensation of N,N′-diisopropylthiourea and isobutyroin. 1,3,4,5-Tetraisopropyl-2-oxoimidazoline (6a), 1,3,4,5-tetraisopropyl-2- selenoimidazoline (6c) and 1,3,4,5-tetraisopropyl-2-telluroimidazoline (6d) were obtained from 2,3- dihydro-1,3,4,5-tetraisopropylimidazol-2-ylidene and dinitrogen oxide or selenium and tellurium, respectively. The crystal structure analyses revealed the presence of the A-type rotamer for 6a while for 6c a paddlewheel-like orientation of the isopropyl substituents was found (I type). In crystals of 6b, both A- and E-type molecules are present while in solution at room temperature the I-type rotamer is detected. A dynamic 1 H and 13 C{ 1 H} NMR study of 6b in the range of 185.5 to 423.3K revealed a temperature-dependent rotation of the isopropyl substituents (ΔH‡ = 15:7(9) kcal mol -1 , ΔS‡ = -5(3) calK -1 mol -1 , ΔG‡ = 17:2(9) kcal mol -1 ) with I as the rotamer of lowest energy. This result is confirmed by MO calculations which indicate A and C being the next stable rotamers. The barrier of rotation of the isopropyl substituents about the C-N bond from I to C (B3LYP ΔH‡ =13:7 kcal mol -1 ,ΔG‡ =15:4 kcal mol -1 ) is slightly lower than that about the C-C bond from I to G.
Type of Medium:
Online Resource
ISSN:
1865-7117
,
0932-0776
DOI:
10.5560/znb.2014-4189
Language:
English
Publisher:
Walter de Gruyter GmbH
Publication Date:
2014
detail.hit.zdb_id:
2078109-X
detail.hit.zdb_id:
124635-5
