1995 R.U. Lemieux Award Lecture Ketenes and bisketeness: organic chemistry in microcosm

1996 ◽  
Vol 74 (4) ◽  
pp. 457-464 ◽  
Author(s):  
Annette D. Allen ◽  
Jim D. Colomvakos ◽  
Ian Egle ◽  
Ronghua Liu ◽  
Jihai Ma ◽  
...  
Keyword(s):  
Organic Chemistry ◽  
Key Words ◽  
Chemical Shifts ◽  
Carbon Suboxide ◽  
Nmr Chemical Shifts

Silyl substituents stabilize ketenes, and permit the preparation of persistent bisketenes, which show characteristic 13C, 17O, and 29Si NMR chemical shifts. The structures and conformations of bisketenes have been examined, as well as their interconversion with cyclobutenediones. A tetraketene has been prepared, and the hydration reactivity of carbon suboxide has been measured. Key words: bisketenes, structures and conformations; cyclobutenedione interconversion.

Carbon-13 chemical shifts of alkene carbons in 2-acylidene-3,5-diaryl-2,3-dihydro-1,3,4-thiadiazoles and related benzothiazoles and -selenazoles, and their relationship to other push-pull alkenes

1996 ◽  
Vol 74 (7) ◽  
pp. 1329-1334 ◽  
Author(s):  
Jennifer L. Mueller ◽  
Martin S. Gibson ◽  
J. Stephen Hartman
Keyword(s):  
Chemical Shift ◽  
Key Words ◽  
Chemical Shifts ◽  
Charge Delocalization ◽  
Nmr Chemical Shifts ◽  
Charge Polarization

Carbon-13 chemical shifts of alkene carbons are observed in the ranges 78–109 ppm (Cα) and 154–164 ppm (Cβ) for a series of 11 2-acylidene-3,5-diaryl-2,3-dihydro-1,3,4-thiadiazoles, 3 2-acylidene-3-alkyl-2,3-dihydrobenzothiazoles, and 2 2-acylidene-3-alkyl-2,3-dihydrobenzoselenazoles of known geometry, indicating appreciable charge polarization in these compounds as in other push–pull olefins. Substitution that promotes more extensive charge delocalization results in the Cα signal shifting to the higher-frequency end of the chemical shift range. The observed shifts are compared with those calculated according to the Pretsch scheme. Key words: carbon-13 NMR, chemical shifts, push–pull olefins, 1,3,4-thiadiazoles, benzothiazoles, benzoselenazoles.

Assigning structures to diastereomeric aliphatic α,α'-dibromo ketones

2002 ◽  
Vol 80 (4) ◽  
pp. 413-417 ◽  
Author(s):  
Masood Parvez ◽  
SM Humayan Kabir ◽  
Ted S Sorensen ◽  
Fang Sun ◽  
Brian Watson
Keyword(s):  
Liquid Chromatography ◽  
Key Words ◽  
Crystal Structures ◽  
Chemical Shifts ◽  
Gas Liquid Chromatography ◽  
X Ray ◽  
Nmr Chemical Shifts ◽  
H Nmr ◽  
Dibromo Ketones

X-ray crystal structures are reported for two symmetrical aliphatic α,α'-dibromo ketones: a meso diastereomer of 3,5-dibromo–2,2,6,6-tetramethylheptan-4-one, and a rac isomer of 4,6-dibromo–2,2,3,3,7,7,8,8-octamethylnonan-5-one. Using these secure assignments and a previously confirmed structure for the diastereomers of 2,4-dibromopentan-3-one, we show in this study that gas-liquid chromatography (GLC) retention times (meso > rac) can be used to confidently assign the diastereomers for a range of symmetrical and unsymmetrical aliphatic α,α'-dibromo ketones. 1H NMR chemical shifts for the >CHBr hydrogen(s) can also be corroboratively used for assignment purposes (δracH > δmesoH).Key words: α,α'-dibromo ketones, X-ray crystal structures, GLC retention times, isomer assignment

Relativistic and Dynamic effects are needed to correctly model the 1H NMR Chemical Shifts of an Iridium Polyhydride Cluster

2020 ◽  
Author(s):  
Abril C. Castro ◽  
David Balcells ◽  
Michal Repisky ◽  
Trygve Helgaker ◽  
Michele Cascella
Keyword(s):  
1H Nmr ◽  
Chemical Shifts ◽  
Dynamic Effects ◽  
Nmr Chemical Shifts

Accurate prediction of 195Pt NMR chemical shifts for a series of Pt(ii) and Pt(iv) antitumor agents by a non-relativistic DFT computational protocol

2014 ◽  
Vol 43 (14) ◽  
pp. 5409-5426 ◽  
Author(s):  
Athanassios C. Tsipis ◽  
Ioannis N. Karapetsas
Keyword(s):  
Dft Calculations ◽  
Anticancer Agents ◽  
Antitumor Agents ◽  
Chemical Shifts ◽  
Accurate Prediction ◽  
Nmr Chemical Shifts ◽  
Relativistic Dft ◽  
Square Planar ◽  
Wide Range ◽  
Computational Protocol

Exhaustive benchmark DFT calculations reveal that the non-relativistic GIAO-PBE0/SARC-ZORA(Pt)∪6-31+G(d)(E) computational protocol predicts accurate 195Pt NMR chemical shifts for a wide range of square planar Pt(ii) and octahedral Pt(iv) anticancer agents.

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