Origin, group

The four carbon atoms of the butanoyl group originate m two molecules of acetyl coenzyme A Carbon dioxide assists the reaction but is not incorporated into the prod uct The same carbon dioxide that is used to convert one molecule of acetyl coenzyme A to malonyl coenzyme A is regenerated m the decarboxylation step that accompanies carbon-carbon bond formation... 

Bonds attached to a functional group origin or 1, 2, or 3 removed can be disconnected. 

Appendage. A structural subunit consisting of one or more carbon atoms and their substituents which is bonded to a ring or functional group origin. 

Functional Group Origin. The atom to which a functional group is attached. 

Boron trifluoride etherate, is also a good catalyst for this hydride transfer to chalcone. Unlike triphenylmethyl perchlorate, however, chalcone is able to enter Michael additions with the 1,5-diketone followed by eliminations leading to unexpected products, e.g., 3-benzyl-2,4,6-triphenylpyrylium from 2-carbethoxy-l,3,5-tri-phenylpentane-l,5-dione and chalcone the benzyl group originates from chalcone, the elimination product being ethyl benzoylacetate. ... 

The net effect of the addition/elimination sequence is a substitution of the nucleophile for the -Y group originally bonded to the acyl carbon. Thus, the overall reaction is superficially similar to the kind of nucleophilic substitution that occurs during an Sn2 reaction (Section 11.3), but the mechanisms of the two reactions are completely different. An SN2 reaction occurs in a single step by backside displacement of the Leaving group a nucleophilic acyl substitution takes place in two steps and involves a tetrahedral intermediate. 

The prindple of equal reactivity of functional groups originates in the comparison by Flory of the results obtained for monoesterifications and polyesterifications. This means that it is particularly important to check whether Flory hypotheses are corred and whether the study of a polyesterification must be limited to the last stages of the reaction. 

In nature, aminotransferases participate in a number of metabolic pathways [4[. They catalyze the transfer of an amino group originating from an amino acid donor to a 2-ketoacid acceptor by a simple mechanism. First, an amino group from the donor is transferred to the cofactor pyridoxal phosphate with formation of a 2-keto add and an enzyme-bound pyridoxamine phosphate intermediate. Second, this intermediate transfers the amino group to the 2-keto add acceptor. The readion is reversible, shows ping-pong kinetics, and has been used industrially in the production ofamino acids [69]. It can be driven in one direction by the appropriate choice of conditions (e.g. substrate concentration). Some of the aminotransferases accept simple amines instead of amino acids as amine donors, and highly enantioselective cases have been reported [70]. 

For carbenes or carbenoids of the type R—C—R there is another aspect of stereochemistry. When these species are added to all but symmetrical alkenes, two isomers are possible, even if the four groups originally on the double-bond carbons maintain their configurations ... 

Chemically bonded layers are prepared by reacting silica gel with various functionalized organosilane reagents forming siloxane Ssonds with some of the silanol groups originally present on the silica surface (10,23,71-77). Chemically bonded siloxane layers... 

Colic is also a symptom of lead poisoning in children. EPA (1986a) has identified a LOAEL of approximately 60-100 pg/dL for children. This value apparently is based on a National Academy of Sciences (NAS 1972) compilation of unpublished data from the patient groups originally discussed in Chisolm (1962, 1965) and Chisolm and Harrison (1956) in which other signs of acute lead poisoning, such as severe constipation, anorexia, and intermittent vomiting, occurred at 60 pg/dL. 

Let us now assume momentarily that the elastomers are perfect, in the sense that all functional groups (originally present in equivalent amounts) have reacted in such a manner that no sol exists. Under such idealized conditions, each molecule of monohydroxy PPO will in effect produce one inactive junction. (Strictly speaking, i molecules of monohydroxy PPO can produce somewhat more than i inactive junctions.) Thus, the concentration of junctions in the network becomes about 0.073 mole/kg instead of 0.100 mole/kg (Table II). As each junction gives 3/2 chains, the modulus, after equating h to zero in eq 1, is given by... 

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