Alpha a-elimination

Rossol I, A Ptihler (1992) The Corynebacterium glutamicum aecD gene encodes a C-S lyase with alpha-beta-elimination activity that degrades aminoethylcysteine. J Bacteriol 174 2968-2977. 

ALPHA-ELIMINATION (a-ELIMINATION) ALPHA EXPULSION ALPHA PARTICLE Alternant,... 

This dehydrohalogenation is called an alpha elimination (a elimination) because the hydrogen and the halogen are lost from the same carbon atom. The more common dehy-drohalogenations (to form alkenes) are called beta eliminations because the hydrogen and the halogen are lost from adjacent carbon atoms. 

In the a-elimination mechanism (39) as shown in Equation 9, hydrogen extraction by the base alpha to the sulfur results in formation of a carbanion which may rearrange via route a or b c to give cysteine and a thioaldehyde which decomposes in alkaline solution to an aldehyde and hydrogen sulfide. Thus, the stoichiometry of this reaction is (Equation 10) ... 

Alpha (a) carbon (Sections 8.1, 19.2B) In an elimination reaction, the carbon that is bonded to the leaving group. In a carbonyl com-pxjund, the carbon that is bonded to the carbonyl carbon. 

The process is called a-elimination because a hydrogen at the alpha carbon at the metal is being eliminated (if we regard the product as a metalla-alkene the... 

The fluorine-destabilised multiple bonds also add nucleophiles easier than their chlorine analogs (ref. 6) and the direction of addition is opposite From nucleophilic alpha-addition to fluorine and beta to chlorine results the relative ease of fluorine substitution inspite of the strong CF-bond, whereas the beta-adducts to chloroacetylenes form triple bonds by a-elimination and rearrangement (ref. 7, Scheme 3). 

Chemists often call the carbon atom that bears the leaving group (e.g., the halogen atom in the previous reaction) the alpha (a) carbon atom and any carbon atom adjacent to it a beta (j8) carbon atom. A hydrogen atom attached to the /3 carbon atom is called a j8 hydrogen atom. Since the hydrogen atom that is eliminated in dehydrohalogenation is from the j8 carbon atom, these reactions are often called fi eliminations. They are also often referred to as 1,2 eliminations. 

Elimination The position bearing the unpaired electron is called the alpha position. In an elimination step, a double bond forms between the alpha (a) and beta (P) positions. As a result, a single bond at the P position is cleaved, causing the compound to fragment into two pieces. 

The biologically active form of vitamin Bg is pyridoxal-5-phosphate (PEP), a coenzyme that exists under physiological conditions in two tautomeric forms (Figure 18.25). PLP participates in the catalysis of a wide variety of reactions involving amino acids, including transaminations, a- and /3-decarboxylations, /3- and ") eliminations, racemizations, and aldol reactions (Figure 18.26). Note that these reactions include cleavage of any of the bonds to the amino acid alpha carbon, as well as several bonds in the side chain. The remarkably versatile chemistry of PLP is due to its ability to... 

Half-life is the time taken to decrease the concentration of a drug to one-half its original value. There may be several phases in the elimination, and the most common is the so-called beta-phase. Alpha-phase is a distribution phase and gamma-phase is the terminal phase when the drug is finally leaving the tissues. 

The use of this direct oxide reduction process is replacing fluoride reduction as it eliminates neutron exposure to operating personnel (alpha particles from plutonium decay have sufficient energy to eject neutrons from fluorine by the a,n reaction) and eliminates reduction residues which require subsequent recovery. 

This experiment eliminated the plum pudding model as a possible structure of the atom. But what did an atom look like Rutherford figured that the only way to make alpha particles bounce backward... 

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