Substituents isopropyl

Triazines pose rather more of a problem, probably because the carbons are in an effectively oxidized state so that no metaboHc energy is obtained by their metaboHsm. Very few pure cultures of microorganisms are able to degrade triazines such as Atrazine, although some Pseudomonads are able to use the compound as sole source of nitrogen in the presence of citrate or other simple carbon substrates. The initial reactions seem to be the removal of the ethyl or isopropyl substituents on the ring (41), followed by complete mineralization of the triazine ring. 

Carbon atom of the methyl group with the highest A8 (isopropyl substituent). 

Another example of a molecular change resulting in a sharp drop in i.s.a. is illustrated by comparing tolamolol with the second molecule in the table. We see that the change is the replacement of the N-isopropyl substituent by an N-aryloxyetbyl residue. 

Methyl isobutyl ketone was reduced with (- )-menthol-LAH in ether to give the (+ )-(S)-carbinol (53) in low optical yield. Methyl neopentyl ketone was similarly reduced to the (-I- )-carbinol, although pinacolone was reduced to only racemic alcohol. Maximum stereoselectivity in the reduction of both ketones and alkenynols was obtained with a 2 1 (-)-menthol-LAH reagent. The observed low stereoselectivity was attributed mainly to insufficient interaction of the remote isopropyl substituent on the menthyl group with the substituents on... 

The preferred stereochemistry arises from the transition state that minimizes interaction between the ethynyl and isopropyl substituents. This stereoselectivity is revealed in the rearrangement of 11 to 12. 

The benzoyl radical from initiator III is more reactive than the parasubstituted benzoyl radical from initiator II. The isopropyl substituent stabilizes the benzoyl radical and make it less reactive. 

The corresponding chemistry of analogous niobium complexes was inhibited by the requirement of a more complicated synthetic approach for the isolation of the niobaziridine hydride. The use of the isopropyl substitued —N(Pr )Ar amido ligand proved unsuitable for the stabilization of [Nb(H) N(P )Ar 2(ri -Me2CNAr)] because of insertion into the Nb—H bond. °2 These difficulties were overcome with use of the N(CH2Bu )Ar substituent and a synthetic approach based upon [Nb(O) N(CH2Bu )Ar 3]3 which enabled the isolation of [Nb(H) N(CH2Bu )Ar 2( ri -CH(Bu )=NAr)] via reduction. The synthesis of this species has opened routes to some unusual chemistry as shown in Scheme 6.5. ... 

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