Assignment of ring size in isopropylidene acetals by 13C N.M.R.

Cyclic isopropylidene acetals containing 5,6 and 7-membered rings can be distinguished by measurement of the ¹³C chemical shifts of the acetal carbon and the methyl groups.     

Trioxaphosphocanes-1,3,6,2, etude par R.M.N. (13C, 1H, 31P et stereochimie

The stereochemistry of several 2-R-1,3,6,2-trioxaphosphocanes (R = Cl, OCH₃, CH₃, N(CH₃)₃ has been investigated by ¹H, ¹³C and ³¹P n m r spectroscopy.     

Fourier 13C NMR and PMR including 13C satellites of oriented cyanopropyne

Fourier ¹³C and proton NMR spectra of cyanopropyne partially oriented by a nematic phase have been recorded and interpreted. It is shown that more accurate measurements are obtained much more rapidly by observing ¹³C satellites by Fourier PMR than by direct observation of the ¹³C spectrum. The geometry has been extracted from direct couplings; a small but systematic discrepancy with microwave spectroscopy is observed for the carboncarbon bond lengths.     

13C high-resolution NMR study of undoped polyacetylene

¹³C NMR spectra of undoped polyacetylene,(CH)_x, have been measured. The existence of 3.4 mol% methylene moieties as defects in the (CH)_x chains has been observed in trans-(CH)_x. Measurements of partially cis-to-trans isomerized (CH)_x suggest the existence of isolated cis regions.     

13C NMR-spectroscopy of polymethoxyxanthones

The ¹³C NMR chemical shifts of eight methoxy-xanthones are reported. Methoxy substituent effects depending on substituent position as well as on shielded ring carbon position have been evaluated. Methoxy substituent increments for xanthones are proposed.     

13C NMR of pterocarpans

¹³CNMR spectra of eight pterocarpans are reported Assignments are based on multiplicities and second-order features in off-resonance decoupled spectra and on chemical shifts in model compounds. Comparison of the degree of long-range (C, H) coupling in ¹H-coupled spectra is found useful     

The case for a revised structure for hypophyllanthin - an analysis of the 13C N.M.R. spectra of aryltetralins

A revised structure for hypophyllanthin is proposed on the basis of its ¹³C n.m.r. spectrum. ¹³C n.m.r. spectra also support the previously proposed structure for nirtetralin and assist in the structural elucidation of a new aryltetralin lignan.     

13C NMR spectrum of coumarin

Summary The positions of the signals from the C₃, C₅, C₆, and C₇ carbon atoms in the¹³C NMR spectrum of coumarin have been established with the aid of information obtained from the¹³C NMR spectra of [3-D]-, [4-D]-, and 7-methoxycoumarins and by the use of an additive calculation based on the increments of the methoxy group in the¹³C NMR spectrum of anisole.M. V. Lomonosov Moscow State University Scientific-Research Institute of Pharmacology, Academy of Medical Sciences of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 458–462, July–August, 1975.     

NMR 13C study of the structure of polyethyleneimine

The NMR ¹³C (CMR) spectrum of high molecular weight (M = 20,000) branched polyethyleneimine (PEI) obtained by polymerization of ethyleneimine (EI) in aqueous and alcoholic solutions at 50° with 1,3-dichloropropanol as initiator, contains 8 lines. The lines were identified using CMR spectra of model compounds, i.e. linear PEI, regularly branched PEI, diethylenetriamine and ethyleneimine pentamer. It has been shown that the deshielding effect of the nitrogen atoms on the α-atoms of carbon decreases in the folowing order: N_tert > N_sec > N_prim; with the atoms of carbon in the β-position, the effect increases in the opposite order.A quantitative estimation has been made of the distribution of the diads of elementary units containing the same and different nitrogen atoms. The data have been used to draw some conclusions about the structure of the PEI macromolecule.     

Microwave spectra of tetrahydroselenophene-α13C, -β13C and molecular ring structure

Microwave spectra of isotopic species α-¹³C and β-¹³C of tetrahydroselenophene molecules have been investigated and rotational constants determined: A = 5608.98 Mc, B = 2819.532 Mc, C = 2022.624 Mc forα-¹³C isotopic species and A = 5695.94 Mc, B = 2770.714 Mc, C = 2009.166 Mc for β-¹³C isotopic species. The r_s-ring structure was found to be Se-C₂ = 1.963 Å, C₂-C₃ = 1.549 Å, C₃-C₄ = 1.527 Å, ∠C₅SeC₂ = 90° 44', ∠SeC₂C₃ = 104° 58', ∠C₂C₃C₄ = 106° 52', the angle of twist = 29° 44'.     

13C NMR spectroscopy of cyclopentenpoliols

The ¹³C NMR spectral parameters of eleven cyclopentenpoliols are discussed. Chemical shift criteria to distinguish isomeric 3' and 4' monodeoxy eucommiols have been clearly established.     

29Si and 13C NMR spectra of permethylpolysilanes

²⁹Si, ¹³C and ¹H NMR spectra are reported for the series of linear permethylpolysilanes Me(SiMe₂)_nMe where n = 1 to 6, for the cyclic permethylpolysilanes (Me₂Si)_n where n = 5 to 8, and for a few related compounds. For linear polysilanes the ²⁹Si and ¹³C chemical shifts can be accurately calculated from simple additivity relationships based on the number of silicon atoms in α, β, γ and δ positions. Adjacent (α) silicon atoms lead to upfield shifts in the ²⁹Si and ¹³C resonances, whereas more remote silicon atoms lead to downfield shifts. The ²⁹Si chemical shifts of the polysilane chains are linearly related to the ¹³C shifts of the carbon atoms attached to the silicon. The ²⁹Si and ¹³C resonances of the cyclic silanes deviate from this relationship. Ring current effects arising from σ delocalization are suggested as an explanation for the deviations. Proton-coupled ²⁹Si NMR spectra are reported for Me₃SiSiMe₃ and for (Me₂Si)_n, n = 5 to 7.     

Vitamin C—A 13C magnetic resonance study

The pH dependence of the ¹³C chemical shifts of ascorbic acid has been measured and interpreted in terms of protonation sites. The transition of the dimer of dehydroascorbic acid into the hydrated monomer form is monitored by ¹³C spectroscopy.     

13C13C spin spin coupling constants in azulenes

[4-¹³C]- Azulene and [4-¹³C]-4-methylazulene have been synthesized. The ¹³C¹³C spin coupling constants have been measured and interpreted in terms of πMO theory.