Group isotopes

Mechanism Kinetic" Order P-Hydrogen Exchange Faster Than Elimination General or Specific Base Catalysis hAd Electron Withdrawal atCp Electron Release at C Leaving- Group Isotope Effect or Element Effect... 

Vitullo, V. P., Logue, E. A. Cyclohexadienyl cations. 6. Methyl group isotope effects in the dienone-phenol rearrangement. J. Am. Chem. Soc. 1976, 98, 5906-5909. 

Leaving group isotope effects have been measured for elimination from dimethylsulphonium - - and trimethylammonium salts - making use of the natural abundance of the elements. The eliminated dimethyl sulphide is analysed directly by mass spectrometry while the eliminated tri-methylamine is usually converted into nitrogen by the Kjeldahl method before analysis - . ... 

LEAVING GROUP ISOTOPE EFFECTS FOR SOME E2 REACTIONS ... 

Internal standards can be considered under four major groups isotope, homolog, generic, and chemically unrelated. To some extent the type of internal standard dictates its applicability. 

Mechanism Kinetic order Hydrogen exchange faster than elimination General or specific base catalysis knlko Electron withdrawal atC- Electron release or C-o" Leaving group isotope effect or element effect... 

Irradiating mesitylene with near-ultraviolet light leads to a shift of methyl groups. Isotopic labeling experiments have shown that the apparent methyl migration is really the ring rearrangement ... 

TLC has been used in the study of many homopolymers polystyrene, poly(methyl methacrylate), poly(ethylene oxide), polyisoprene, poly(vinyl acetate), poly(vinyl chloride) and polybutadiene. Their molecular weight, molecular-weight distributions, microstructure (stereo-regularity, isomerism and the content of polar end groups), isotope composition and branching have been studied. For copolymer characterisation (e.g. purity and compositional inhomogeneity), random copolymers such as styrene-methacrylate, and block copolymers such as styrene-butadiene, styrene-methyl methacrylate and styrene-ethylene oxide have been separated. A good review article on polymers... 

PVME-PS-d in the other hand are series of blends diich behave similarly, These results clearly show that the increase of the miscibility of PS and PVME upon deuteration is almost completely the result of the deuteration of the phenyl group. Isotopic substitution of the aliphatic chain atoms has a negligible effect. The phenyl rings of PS must be involved in the specific interactions with the PVME chains that contribute to the miscibility. These findings corroborate well those of previous studies by Fourier-transformed infrared spectroscopy (21, 22)... 

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