¹³C Nuclear Magnetic Resonance Studies. XX. ¹³C Shieldings of Several Allyl Alcohols. Geometric Dependence of ¹³C Shieldings

Abstract

The I3C spectra of 21 methyl-and halo-substituted 2-propenols have been determined. The shielding data are discussed with particular emphasis on their dependence on the orientation of the 3-halo substituents. Linear regression analyses of the results gave sets of additive parameters which correlate the shieldings with reasonable precision ( < 1 p.p.m.). A similar set of parameters has been generated from the published data for acyclic alkenes: these parameter sets are intercompared. The results of complete analysis of the proton spectra of most of the alcohols are also presented.On a determine le spectre au 13C de 21 derives methyles et halogenes du 2-propenol. On discute des donntes de blindage en insistant particulierement sur leur effet dans I'orientation des substituants halogenes en position-3. Les analyses de regression lineaire des rCsultats ont don& des ensembles de paramttres additifs qui nous fournissent les blindages avec une precision raisonnable (< l p.p.m.). Un ensemble similaire de paramttres a CtC tire des donnCes publikes pour les alctnes acycliques: on compare ces parametres avec ceux qu'on a obtenus. On presente aussi les resultats de I'analyse compltte des spectres de protons de la plupart des alcools.Canadian Journal of Chemistry, 50. 1361 (1972) IntroductionIn an earlier part of this series, 13C n.m.r. spectra of several unsaturated aliphatic systems were discussed and the results of an examination of a$-unsaturated carboxylic acids and esters compared with earlier data (1). These results clearly showed that olefinic 13C shieldings exhibit a marked dependence on the orientation of substituents bonded to the olefinic carbons. Furthermore, these shieldings were correlated by a linear expression entirely analogous to that employed for acyclic saturated hydrocarbons(2),

Synthesis and structural characterization of syndiotactic trans‐1,2 and cis‐1,2 polyhexadienes

“…1) H6 would show a three bond correlation with an aliphatic carbon (C4) and not with an olefinic carbon as in the case of a 1,2 structure. The proposed assignment is also in agreement with the chemical shifts calculated with the Brouwer and Stothers approach14 from the experimental chemical shifts of the 1,2 syndiotactic polybutadiene olefinic carbons (141.5 and 112.3 ppm for C3 and C4, respectively). By adding an ethyl group, a βπ (−7.1 ppm) plus a γπ (−1.9 ppm) effect must be considered on C3 and an απ (11.0 ppm) plus a βσ (6.0 ppm) effect on C4.…”

“…Moreover, the experimental chemical shifts are in agreement with the those calculated with the Brouwer and Stothers approach14 starting from the experimental data of cis ‐1,2 syndiotactic polypentadiene3 (137.06 and 122.98 ppm for C3 and C4, respectively). By adding a methyl group, a γπ (−1.9 ppm) effect was considered on C3 and a βσ (6.0 ppm) effect on C4.…”

Thermally induced polymerization of isobutylene in the presence of SnCl4: Kinetic study of the polymerization and NMR structural investigation of low molecular weight products

“…In the cited article, we assigned the lines to terminal structure D (Scheme ) and mentioned that a similar structure, [CH 2 C(CH 3 )C(CH 3 ) CH(CH 3 ) 2 ] (E‐type) cannot be excluded. However, we preferred structure D because of better agreement with chemical shifts calculated using empirical parameters obtained by regression analysis of olefin carbon shifts in substituted alkenes36, 42 and because of a good agreement with chemical shifts of the model olefin,43 (CH 3 ) 2 CC(CH 3 ) CH 2 CH 3 . Günther et al39 assigned these lines to terminal structure E; however, the recently measured pulsed‐field gradient (PFG) heteronuclear multiple bond correlation (HMBC) 2D NMR spectra44 unambiguously confirmed that lines at 121.5 and 133.3 ppm correspond to terminal structure D. Moreover, PFG HMBC 2D NMR spectra show that structure E will provide lines of two quaternary carbons at 125.3 and 136.6 ppm.…”

The alkaloids of Seneciotriangularis Hook

“…The identity of the Cj-acid component, which must be one of the mono-olefinic CSH,O, possibilities, also followed from the 'H nmr spectrum of A: the absorptions at 6 1.81, 1.96, and 6.08 define an angelate (Z-2-methyl-2-butenoate) unit (2,4,5). (These shifts unambiguously exclude the tiglate (E-2-methyl-2-butenoate) and senecioate (3-methyl-2-butenoate) alternatives.…”