Carbon-13 Nuclear Magnetic Resonance Spectra of Olefins and Other Hydrocarbons

The 15.1 Mc/s I3C n.1n.r. spectra of 34 a,p-unsat~~rated carbonyl compounds have been obtained and the chemical shifts of the olefnic and carbonyl carbon nuclei are reported. Esamples were drawn from the acyclic and five-and six-membered ring alicyclic series. A few aldehydes are included although most of the con~pounds are ketones. In the case of compounds ass~~rned to be planar, variations of the olefinic shieldings with alkyl substitution parallel those observed previously for olefinic hydrocarbons. The key factor governing the chemical shifts of the carbo~lyl-carbon nuclei appears to be the extent of conjugation in a given system. Conseq~~ently, the 13C results prov~de evidence for steric interference to coplanarity in the hi~ldered systems. This approach is compared with other methods of estimating the extent of steric inhibition of co~ljugation and its merits are assessed.

Section: Introductionsupporting

confidence: 54%

Section: Introductionmentioning

confidence: 99%

¹³C N.M.R. STUDIES: PART VI. CARBON-13 SPECTRA OF α,β-UNSATURATED CARBONYL COMPOUNDS

Marr¹,

Stothers²

1965

“…Up-field shifts are found also for the a-chlorinated ketones, presumably for the same reason and, in addition, the observed shifts to higher field are approxi~nately additive for each additional halogen atom. The feature of additivity of substituent effects on C13 chenlical shifts has already been noted for a number of systenls (4)(5)(6)(7)(8)12). Further exanlples of the effects of chlorine substitution are discussed later.…”

Section: Atoll1 (D)mentioning

confidence: 59%

“…a t the low-field end of the C13 spectral region. Some olcfinic carbons (4, 3, 8) absorb within the upper portion of this region, as do oximes (A), carboil \ / disulphide, and the central carbon of the allenic structure, ,C=C=C (8) ; otherwise, \ there is no interference with the C13 resonances of other classes of compounds for which data are preseiltly available. As discussed later, it seeins liltely that a distinction between carbonj~l peaks and those due to other carbons inay be made on the basis of preferential solvent effects.…”

Section: Generalmentioning

confidence: 99%

C¹³ CHEMICAL SHIFTS IN ORGANIC CARBONYL GROUPS

Stothers¹,

Lauterbur²

1964

160

“…25. 2Holder of NRCC Scholarships, 1966 Retcofsky and Friedel (6) noted the general trends exhibited by olefinic shieldings upon alkyl substitution but, for practical reasons, these authors did not investigate the shieldings of carbons bonded to the olefinic nuclei. In our previous report, we noted that the carboxyl carbon shieldings of acrylic acids and esters are essentially independent of substituent orientation whereas olefinic methyl carbons exhibit a marked geometrical dependence.…”

Section: Introductionmentioning

confidence: 99%

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

Brouwer¹,

Stothers²

1972

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),