Determination of rotational barriers in four thioamides

Hobson, R. F.; Reeves, L. W.; Shaw, Kenneth N.F.

doi:10.1021/j100629a010

Cited by 27 publications

(13 citation statements)

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“…Both imply higher S polarisation than O. Also, 'H NMR studies for the hindered NH, rotation barriers [14,15] show that the thioamides have higher barriers than the corresponding amide by about 8.5kJmoI -1 . However, the NC bonds in gaseous HCONH 2 and HNSNH 2 are effectively identical in length, implying equal CN bond order [4], Thus we reconsider the charge distributions in amides and thioamides, ureas and thioureas and their methylated derivatives.…”

Section: Introductionmentioning

confidence: 98%

“…The principal NQCC (\") at 14 N in formamide [2,3] is -3.848±0.004MHz while that in thioformamide is thought to be -4.2±0.6 MHz or alternatively -3.7±0.4 MHz [4], a poorly determined comparison. However, the NQCC for urea (-3.51) [5 -8] is higher than thiourea (-3.12MHz) [9], and this has been attributed to higher resonance in the latter than in the former [10], It was assumed that the 0932-0784 / 96 / 0500-460 $ 06.00 © -Verlag der Zeitschrift für Naturforschung, D-72072 Tübingen higher at l4 N implies higher localisation.…”

Section: Introductionmentioning

confidence: 99%

“…These studies concentrate on simple amides and thioamides, and in particular with formamide and thioformamide, acetamide, urea and thiourea and their methylated derivatives. The purpose of the investigation is to reconsider the anomalous 14 N quadrupole coupling in these molecules. The background to this matter is as follows.…”

Section: Introductionmentioning

confidence: 99%

“…C 2.5 N 3.0, O 3.5 and S 2.5 all from the Pauling scale [1], but other scales exist with similar interrelationships. Each of the above molecules has a 14 N centre and either a 17 0 or 33 S centre, all being quadrupolar. The gas phase and solid state 14 …”

Section: Introductionmentioning

confidence: 99%

“…Each of the above molecules has a 14 N centre and either a 17 0 or 33 S centre, all being quadrupolar. The gas phase and solid state 14 …”

Section: Introductionmentioning

confidence: 99%

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The Charge Distribution in Amides and Thioamides by Nuclear Quadrupole Coupling, Dipole Moments and Electronic Structure Calculations

Palmer

Sherwood

1996

Zeitschrift Für Naturforschung A

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The nuclear quadrupole coupling constants from microwave spectroscopy (MW) and quadrupole resonance (NQR) for amides and thioamides are discussed in relation to Hartree-Fock calculations with and without Moller-Plesset correlation effects. The view that the larger dipole moments from thioamides than the corresponding amides is a function of enhanced resonance in the former is discussed and (in effect) confirmed by the present procedures. The principal mechamism seems to be the push/pull K/C effects of the N atom with respect to the CO and CS groups, with S being a better o-donor than O; however, the effect is still present with formamidine where no electronegativity effects are important, so the overall effect is the 2,1,17t-electron contribution to the allylic system from N, C, O(S). The use of localised MO's and NO's is described, and the centroid positions are discussed in relation to the polarity of the bonds. The LMO's largely truncate the contributions to each NQCC to the three attached bonds (or 2 bonds + a lone pair orbital at O or S), as is used in the Townes-Dailey procedures. More distant LMO's generally contribute < 0.05 a. u. to the EFG, simplifying the analysis. The effects of 0(or S)-protonation of urea and thiourea is discussed.

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Each of the above molecules has a 14 N centre and either a 17 0 or 33 S centre, all being quadrupolar. The gas phase and solid state 14 …”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

The Charge Distribution in Amides and Thioamides by Nuclear Quadrupole Coupling, Dipole Moments and Electronic Structure Calculations

Palmer

Sherwood

1996

Zeitschrift Für Naturforschung A

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Recent Advances in Atropisomerism

Ōki

1983

Topics in Stereochemistry

348

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Reaktionen von α‐Bromisothiocyanaten

Hussein¹,

Jochims²

1979

Chem. Ber.

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a-Bromisothiocyanate 1 1,2) mit einem P-Wasserstoff spalten HBr zu Vinylisothiocyanaten ab (Produkte 2, 3, 5). Wasser hydrolysiert 1 zu Carbonylverbindungen (7a). Harte Nucleophile greifen 1 am a-C-Atom unter Substitution des Broms an (Produkte 8 -12), weiche Nucleophile lagern sich dagegen an das C-Atom der Isothiocyanatgruppe an (Produkte 14, 19). Verbindungen 1 reagieren mit bifunktionellen Nucleophilen zu Heterocyclen (z. B. Produkte 16, 21). Die chemischen Eigenschaften der z. T. neuen Verbindungsklassen, z. B. der geminalen Diisothiocyanate 12, werden untersucht. Der Alkylidenthioharnstoff 14f zeigt behinderte Rotation um die Amid-CS-N-Bindung (AGg4 = 82.8 kJmol-') und urn die C=N-Doppelbindung (AG& = 52.9 kJmol-'). Reactions of a-Bromoisothiocyanatesa-Bromoisothiocyanates 1 with a hydrogen in P-position eliminate HBr to form vinyl isothiocyanates (products 2, 3, 5). Water hydrolyzes 1 to carbonyl compounds (7a). Hard nucleophiles attack 1 at the a-C-atom with substitution of bromine (products 8 -12), but soft nucleophiles add to the C-atom of the isothiocyanato group (products 14, 19). Compounds 1 react with bifunctional nucleophiles to heterocycles (e. g. products 16, 21). The chemical properties of the classes of compounds, part of which are new, e. g. the geminal diisothiocyanates 12, are examined. The alkylidene thiourea 14f shows hindered rotation around the amide-CS -N bond (ACg4 = 82.8 kJmol-') and around the C = N double bond (AC& = 52.9 kJmol-'). a-Bromisothiocyanate 1 gewinnt man durch radjkalische Bromierung von sekundaren Isothiocyanaten >CH -NCS oder primaren Senfdlen R -CH, -NCS, wenn R eine aktivierende Gruppe wie Aryl oder CO,R ' ist, mit N-Bromsuccinimid (NBS)'v2). Die a-Bromisothiocyanate sind reaktionsfahige bifunktionelle Elektrophile, die mit Nucleophilen an den C-Atomen beiderseits des Stickstoffs reagieren kdnnen, wie die folgenden Umsetzungen der Verbindungen 1 a -f zeigen.Die a-Halogenisothiocyanate l a -c, die ein Wasserstoffatom in P-Stellung zur Senfolgruppe tragen, spalten thermisch oder mit Triethylamin leicht Halogenwasserstoff zu a,&ungesattigten Isothiocyanaten (2, 3, 5) ab3s4). Die HBr-Eliminierung erfolgt so leicht, da8 es manchmal nicht gelingt, die a-Bromisothiocyanate zu isolieren2). aBromierung der im allgemeinen leicht zuganglichen Senfole und anschlienende HBrAbspaltung stellt somit eine einfache Methode zur Darstellung der bisher nur wenig untersuchten Vinylisothiocyanate3 -dar.Durch Addition von Aminen bzw. Hydrazinen erhalt man Vinylthioharnstoffe und Vinylthiosemicarbazide (4a -c) und im Falle 5 das Cyclisierungsprodukt 6'O).

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Determination of rotational barriers in four thioamides

Cited by 27 publications

References 7 publications

The Charge Distribution in Amides and Thioamides by Nuclear Quadrupole Coupling, Dipole Moments and Electronic Structure Calculations

The Charge Distribution in Amides and Thioamides by Nuclear Quadrupole Coupling, Dipole Moments and Electronic Structure Calculations

Recent Advances in Atropisomerism

Reaktionen von α‐Bromisothiocyanaten

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