A-Hydrogen groups

Loss of the a-hydrogen (Group a). Dissociation of the a-hydrogen from the Schiff base leads to a quinonoid-carbanionic intermediate whose structure in depicted in Fig. 14-5. The name reflects the characteristics of the two resonance forms drawn. 

Attack in the conformation 139 which leads to the Z-isomer takes place from the upper surface of the molecule, anti to the trimethylsilyl group. This face is occupied by a hydrogen group. In the conformation 138 which leads to the -isomer, this surface is occupied by a methyl group. The greater steric effect of this group leads to the small... 

The difference between barbituric acid and the natural compounds uracil and thymine is the presence of a keto-group instead of a methyl- or a hydrogen-group in the 6-position of the ring. Barbiturase was first detected by Hayashi and Kornberg 39 in bacteria of the genera Mycobacterium and Corynebacterium and postulated to catalyze a sidereaction in the degradation of pyrimidines. Unfortunately, there are no further data in literature on the substrate specificity and the stereoselectivity of this enzyme, which would allow comparison with the D-hydantoinase, but Kautz and... 

A white solid, m.p. 178 C. Primarily of interest as a brominaling agent which will replace activated hydrogen atoms in benzylic or allylic positions, and also those on a carbon atom a to a carbonyl group. Activating influences can produce nuclear substitution in a benzene ring and certain heterocyclic compounds also used in the oxidation of secondary alcohols to ketones. 

CfiHsNjOs. Red needles m.p. 168-169°C. Soluble in dilute acids and alkalis. Prepared by reduction of picric acid with sodium hydrogen sulphide, ft is used for the preparation of azodyes, which can be after-chromed by treatment with metallic salts owing to the presence of a hydroxyl group ortho to the amino-group. 

Phenols formed by the substitution of a hydrogen atom by a hydroxyl group, OH, in an aromatic ring ( I t)... 

Some of the common aromatics found in crude oil are the simple derivatives of benzene in which one or more alkyl groups (CHg) are attached to the basic benzene molecule as a side chain which takes the place of a hydrogen atom. These arenes are either liquids or solids under standard conditions. 

BUTENE. As shown in Figure 38, a group attached to C-1 can migrate from position 1 to 3 (1,3 shift) to produce an isomer. If it is a methyl group, we recover a 1-butene. If it is a hydrogen atom, 2-butene is obtained. A third possible product is the cyclopropane derivative. The photochemical rearrangement of 1-butene was studied extensively both experimentally [88]... 

Hydroxylamine is derived from ammonia by replacing one hydrogen atom by a hydroxyl group. It is prepared by the electrolytic reduction of nitric acid, using a lead cathode ... 

If alOTU 1 or alom j is a hydrogen, Ih e d eforin anon (r-r,j) is considered lo be zero. Thus, no slrelch-bend inleraciion is defined for XHp groups. The slrelch-bend force con slams are incorporated into lb e program and you canriol modify Ihcm. If R is an alom otb er b y dm gen, tb e values of lhe stretcb -bend force eon si an Is are ... 

Bartlett P A and C K Marlowe 1987. Evaluation of Intrinsic Binding Energy from a Hydrogen-bondi Group in an Enzyme Inhibitor. Science 235 569-571. 

Alternatively, it may bo assumed that the basic ethoxide ion attacks a hydrogen atom of the activated CH, group to yield the carbanion directly ... 

Malonic ester, like acetoacetic ester (Section 111,151), when treated with an equivalent of sodium ethoxide, forms a mono-sodium derivative, which is of great value in synthetical work. The simplest formulation of the reaction is to r rd it as an attack of the basic ethoxide ion on a hydrogen atom in the CH, group the hydrogen atoms in the CHj group are activated by the presence of the two adjacent carbethoxyl groups ... 

Many inorganic and organic compounds possessing labile hydrogen atoms add acrylonitrile readily with the formation of compounds containing a cyancethyl grouping (—CH j. CH2. CN). This reaction is usually known as cyanoelhylation ... 

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