Charge distributions and chemical effects. X. Enthalpies of formation of alkanes, a calculation from 13C nuclear magnetic resonance shifts

1976 ◽  
Vol 54 (13) ◽  
pp. 2085-2088 ◽  
Author(s):  
Hervé Henry ◽  
Sándor Fliszár ◽  
André Julg
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Linear Combination ◽  
Enthalpies Of Formation ◽  
Chemical Effects ◽  
13C Nuclear Magnetic Resonance ◽  
Net Charges ◽  
The Relationship ◽  
Two Parameter ◽  
C Nmr

An analysis of the molecular energy in terms of bond contributions indicates that the latter (εij) can be approximated by a linear combination of the changes in net charges qi and qj. From the equation ΔH(atomization) = ∑εij, and the relationship between 13C chemical nmr shifts and C net charges, it is then possible to derive a two-parameter equation, ΔHf0 = ΔHf0(C2H6) + ν(N–2) + λ∑(Ncc + 1)δeth, which enables the calculation of enthalpies of formation of alkanes CNH2N+2 from 13C nmr shifts (δeth = shift relative to ethane, Ncc = number of CC bonds formed by the C atom whose shift is δeth).

Nuphar thiaspirane sulfoxides. 13C nuclear magnetic resonance determined configuration and utilization in the interconversion of thiaspirane stereochemical types

1978 ◽  
Vol 56 (1) ◽  
pp. 56-61 ◽  
Author(s):  
R. T. LaLonde ◽  
C. F. Wong
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Subsequent Reduction ◽  
13C Nuclear Magnetic Resonance ◽  
Sodium Borodeuteride ◽  
C Nmr ◽  
Nuclear Magnetic

The configuration of the sulfoxide oxygen in syn- and anti-thiobinupharidine sulfoxide was determined by employing the 13C nmr sulfoxidation increments of C-6. Establishment of the 13C nmr line assignments for C-6 included the study of the C-6 and C-6′ deuterated thiobinupharidine and the corresponding sulfoxides. Thermolysis of syn-thiobinupharidine sulfoxide in DMSO and subsequent reduction with sodium borodeuteride in methanol yielded thiobinupharidine, labelled with deuterium only at C-6, and thionuphlutine B, labelled with deuterium at both C-6 and C-6′. Treatment of the anti sulfoxide in xylene or DMSO resulted in no thiobinupharidine or thionuphlutine B. Similarly, syn-neothiobinupharidine sulfoxide gave neothiobinupharidine and a new thiaspirane, thionuphlutine C. These two compounds were not produced from anti-neothiobinupharidine sulfoxide heated in xylene.

13C nuclear magnetic resonance spectra of the spirobenzylisoquinoline alkaloids and related model compounds

1977 ◽  
Vol 55 (18) ◽  
pp. 3304-3311 ◽  
Author(s):  
Donald W. Hughes ◽  
Bala C. Nalliah ◽  
Herbert L. Holland ◽  
David B. MacLean
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Isoquinoline Alkaloids ◽  
Model Compounds ◽  
Related Model ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
C Nmr ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The natural abundance 13C nuclear magnetic resonance spectra of a number of spirobenzylisoquinoline alkaloids and related model compounds have been recorded. The carbon resonances of the alkaloids were assigned by comparison with the spectra of other isoquinoline alkaloids and with those of the model compounds. It has been shown that 13C nmr spectroscopy may be used to differentiate between diastereomers in this series.

15N and 13C nuclear magnetic resonance of deoxydinucleotide monophosphates. II. Protonation of the homo dimers deoxycytidylyl-(3′,5′)-deoxycytidine, thymidylyl-(3′,5′)-thymidine, and deoxyadenylyl-(3′,5′)-deoxyadenosine in dimethyl sulfoxide

1990 ◽  
Vol 68 (11) ◽  
pp. 2033-2038 ◽  
Author(s):  
Giovanna Barbarella ◽  
Massimo Luigi Capobianco ◽  
Luisa Tondelli ◽  
Vitaliano Tugnoli
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Dimethyl Sulfoxide ◽  
Phosphate Group ◽  
Nmr Data ◽  
13C Nuclear Magnetic Resonance ◽  
C Nmr ◽  
Nuclear Magnetic

The preferential protonation sites of the homo dimers deoxycytidylyl-(3′,5′)-deoxycytidine, thymidylyl-(3′,5′)-thymidine, and deoxyadenylyl-(3′,5′)-deoxyadenosine were established by nitrogen-15 and carbon-13 NMR in dimethyl sulfoxide, in the presence of varying amounts of CF3COOH. The nitrogen-15 NMR data show that in d(CpC) the capability of the two N3 nitrogens to accept the proton is slightly different. In d(TpT) and d(ApA) the protonation of the phosphate group leads to significant variations of the chemical shift of the carbons adjacent to phosphorus. Keywords: deoxydinucleotides, protonation, 15N and 13C NMR.

13C nuclear magnetic resonance and Raman investigations of aqueous carbon dioxide systems

1982 ◽  
Vol 60 (8) ◽  
pp. 1000-1006 ◽  
Author(s):  
Theresa M. Abbott ◽  
Gerald W. Buchanan ◽  
Peeter Kruus ◽  
Keith C. Lee
Keyword(s):  
Carbon Dioxide ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Linear Relationship ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Carbonate Ion ◽  
13C Nuclear Magnetic Resonance ◽  
Wide Range ◽  
C Nmr

13C-nmr spectra of carbon dioxide in water are reported for a wide range in pH. Chemical shifts were determined for the following species: CO2(g), CO2(aq), HCO3−(aq), CO32−(aq). A linear relationship was found between the shift of the 13C line and the fraction of carbonate ion calculated to be present, as well as between the ratio of the area under the 1067 cm−1 (carbonate) Raman peak to the sum of the area under the 1067 cm−1 and 1017 cm−1 (bicarbonate) peaks and the fraction carbonate.

scholarly journals Chemical constituents of the physodes of brown algae. Characterization by 1H and 13C nuclear magnetic resonance spectroscopy of oligomers of phloroglucinol from Fucus vesiculosus (L.)

1977 ◽  
Vol 55 (9) ◽  
pp. 1575-1582 ◽  
Author(s):  
James S. Craigie ◽  
A. Gavin McInnes ◽  
Mark A. Ragan ◽  
John A. Walter
Keyword(s):  
Molecular Weight ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Chemical Constituents ◽  
Fucus Vesiculosus ◽  
Resonance Spectroscopy ◽  
Low Molecular Weight ◽  
13C Nuclear Magnetic Resonance ◽  
C Nmr

Alcoholic extracts of Fucus vesiculosus contain small quantities of low molecular weight polyphenols derived from phloroglucinol and 2,2′,4,4′,6,6′-hexahydroxybiphenyl. 1H and 13C nmr were used to identify two of these as 4-(2′′,4′′,6′′-trihydroxyphenoxy)-2,2′,4′,6,6′-pentahydroxybiphenyl and 4-(2′′-(2′′′,4′′′,6′′′-trihydroxyphenoxy)-4′′,6′′-dihydroxyphenoxy)-2,2′,4′, 6,6′-pentanydroxybiphenyl.

Direct non-invasive observation of metabolism in living cells by 13C nuclear magnetic resonance spectroscopy

1980 ◽  
Vol 58 (17) ◽  
pp. 1839-1846 ◽  
Author(s):  
Gerardo Burton ◽  
Robert L. Baxter ◽  
J. Martyn Gunn ◽  
Philip J. Sidebottom ◽  
Paul E. Fagerness ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Anaerobic Metabolism ◽  
Aminolevulinic Acid ◽  
Living Cells ◽  
Resonance Spectroscopy ◽  
Whole Cells ◽  
Non Invasive ◽  
13C Nuclear Magnetic Resonance ◽  
C Nmr

Applications of 13C nmr in following the metabolism and fate of 13C enriched substrates in whole cells are described. Studies on the elaboration of coproporphyrinogens I (2a) and III (2b) from [5-13C]-δ-aminolevulinic acid (1) and [11-13C-porphobilinogen (PBG, 3), in Rhodopseudomonasspheroides and Propionibacteriumshermanii, respectively, the randomization of 13C from [3-13C]-propionate by P. shermanii, the biosynthesis of citrate, gentisalcohol (4), and patulin (5) from [2-13C]-acetate by Penicilliumurticae, and the anaerobic metabolism of [1-13C]-glucose in rabbit erythrocytes are reported.

13C nuclear magnetic resonance studies. 58. 13C spectra of a variety of bicyclo[2.2.2]octane derivatives. Further definition of the deshielding δ effect

1976 ◽  
Vol 54 (6) ◽  
pp. 917-925 ◽  
Author(s):  
J. B. Stothers ◽  
C. T. Tan
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nmr Spectra ◽  
Magnetic Resonance Studies ◽  
13C Nuclear Magnetic Resonance ◽  
Definition Of ◽  
C Nmr ◽  
Nuclear Magnetic

The 13C nmr spectra of 35 bicyclo[2.2.2]octane and -octene derivatives have been determined to extend our examinations of the effects of stereochemistry on the shieldings of closely neighboring carbons. This series includes a variety of methyl substituted bicyclooctanols and -octenols as well as the corresponding hydrocarbons and some bicyclooctanones. With the bicyclo[2.2.2]octane skeleton it is possible to examine an array of systems having substituents separated by three and four bonds in a variety of orientations. The interactions, termed γ and δ effects, respectively, produce distinctive shielding variations which are useful for stereochemical elucidations. Particularly interesting are the pronounced shifts observed for the carbons bearing closely neighboring substituents. Characteristically, for vicinal substituents, these carbons are shielded while for syn-axial δ interactions, these carbons are deshielded by as much as 8.6 ppm. The results are compared with the trends found in other sterically crowded Systems.

Solvent and α-substituent perturbations of the 2H/1H isotope shifts in the 13C nuclear magnetic resonance of toluene-α-d3

1987 ◽  
Vol 65 (3) ◽  
pp. 534-537 ◽  
Author(s):  
Ted Schaefer ◽  
James Peeling ◽  
Rudy Sebastian
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Refractive Index ◽  
Magnetic Resonance ◽  
Isotope Effect ◽  
Electron Donor ◽  
Chemical Shifts ◽  
Aromatic System ◽  
Expectation Value ◽  
13C Nuclear Magnetic Resonance ◽  
C Nmr

The 2H/1H isotope effect on 13C nmr chemical shifts, nΔ, n being the number of intervening bonds between 2H and 13C nuclei, in toluene-α-d3 is solvent dependent. For example, 1Δ ranges from 817 ppb in CD3OH to 869 ppb in acetone-d6 solutions, a positive number indicating increased shielding in the deuterated species. 1Δ is linearly dependent on a function of the refractive index, nD, of the solvent, allowing extrapolation to nD = 1. The hyperconjugative model, in which the C—D bond is a poorer electron donor to the aromatic system than is a C—H bond, is tested for the substituents CH2D, CHD2, CD3, CHDCH3, CD2CH3, CD(CH3)2, C6H5CHD, and (C6H5)2CD. For these substituents, the negative 5Δ is linearly related to the expectation value of sin2 θ; θ is the angle by which the C—D bond twists out of the benzene plane. The model fails quantitatively for C6H5CD2X (X = Cl, COOH, CN, OH). For X = OH, very large negative 5Δ and 3Δ values are observed. nΔ is also reported for 4-ethyltoluene-α-d3 and benzaldehyde-α-d1. For the latter, all nΔ values are positive other than 5Δ, which vanishes in acetone-d6 solution.

Alkanes with multiple asymmetric centers: synthesis, identification, and 13C nuclear magnetic resonance spectra

1979 ◽  
Vol 57 (4) ◽  
pp. 367-376 ◽  
Author(s):  
Pierre Lachance ◽  
S. Brownstein ◽  
Arthur M. Eastham
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nmr Spectra ◽  
Aliphatic Hydrocarbons ◽  
Capillary Chromatography ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
Capillary Glc ◽  
C Nmr ◽  
Magnetic Resonance Spectra

The identification of aliphatic hydrocarbons containing multiple asymmetric centers can be difficult because of the complexity of the nmr spectra and because in capillary chromatography the diastereomers may be resolved to varying degrees. We suggest that the most effective method for identifying such hydrocarbons is through the pattern of retention times developed by the mixture of diastereomers on a suitable capillary glc column.This paper presents the results of some studies of a series of alkanes having the general form C2H5—(CH—CH3)n—R, where n = 1 to 4, and includes the syntheses and 13C nmr spectra of the compounds.

1H and 13C Nuclear Magnetic Resonance Studies of the Hindered Phencyclone Adducts of Some Smaller Branched N-Alkyl Maleimides: Rigorous Aryl Proton Assignments with High-Resolution Two-Dimensional (COSY45) Spectroscopy, and Anisotropic Shielding Effects and Ab Initio Geometry Optimizations

2005 ◽  
Vol 59 (3) ◽  
pp. 354-365 ◽  
Author(s):  
Ronald Callahan ◽  
Ron Prip ◽  
Navroz Shariff ◽  
Olga Sklyut ◽  
Robert Rothchild ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
High Resolution ◽  
Basis Set ◽  
Nmr Studies ◽  
Alkyl Groups ◽  
13C Nuclear Magnetic Resonance ◽  
C Nmr ◽  
Shielding Effects ◽  
Nuclear Magnetic

Phencyclone, 1, a potent Diels-Alder diene, reacts with a series of N-alkylmaleimides, 2, to form hindered adducts, 3. The 300 MHz 1H and 75 MHz 13C NMR studies of these adducts at ambient temperatures have demonstrated slow rotations on the nuclear magnetic resonance (NMR) timescales for the unsubstituted bridgehead phenyl groups, and have revealed substantial magnetic anisotropic shielding effects in the 1H spectra of the N-alkyl groups of the adducts. The selected N-alkyl groups for the target compounds emphasized smaller branched alkyls, including C3 (isopropyl, a); C4 (isobutyl, b; and t-butyl, c); C5 (n-pentyl, d; isopentyl [isoamyl], e; 1-ethylpropyl, f; t-amyl, g;) and a related C8 isomer (1,1,3,3-tetramethylbutyl [“t-octyl”], h). The straight-chain n-pentyl analog was included as a reference. This present work on the branched N-alkylmaleimide adducts appreciably extends our earlier compilation on the N-n-alkylmaleimide adducts. Key methods for proton assignments included “high-resolution” 1H–1H chemical shift correlation spectroscopy, COSY45. 13C NMR of the adducts, 3, verified the expected number of aryl carbons for slow exchange limit (SEL) spectra of the bridgehead phenyl groups. The synthetic routes involved reaction of the corresponding amines, 4, with maleic anhydride to give the N-alkylmaleamic acids, 5, which underwent cyclodehydration to form the maleimides, 2. Magnetic anisotropic shielding magnitudes for alkyl group protons in the adducts were calculated relative to corresponding proton chemical shifts in the maleimides. Geometry optimizations for the above adducts (and for the N-n-butylmaleimide adduct) were performed at the Hartree-Fock level with the 6–31G* basis set. The existence of different contributing conformers for the adducts is discussed with respect to their calculated energies and implications regarding experimentally observed anisotropic shielding magnitudes.

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