Common Directing Groups

SCHEME 23.7 Directing groups (DGs) for chelate-assisted C-H functionalization. 

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Scheme 23.7 depicts various common directing groups for chelate-assisted C-H functionalizations. Directing groups that coordinate through their N-atom such as pyridines and other heterocycles (la-r) have been most widely used [2, 4, 23]. 

Resonance effects are the primary influence on orientation and reactivity in electrophilic substitution. The common activating groups in electrophilic aromatic substitution, in approximate order of decreasing effectiveness, are —NR2, —NHR, —NH2, —OH, —OR, —NO, —NHCOR, —OCOR, alkyls, —F, —Cl, —Br, —1, aryls, —CH2COOH, and —CH=CH—COOH. Activating groups are ortho- and para-directing. Mixtures of ortho- and para-isomers are frequently produced the exact proportions are usually a function of steric effects and reaction conditions. 

It is the determination of volatile organic compounds produced from natural products that requires separation techniques that allow isolation of stereoisomers. The most commonly determined groups are the terpene and sesquiterpene species present in essential oils, which are used as key indicators of biological factors such as the growth season, geographic location, climate, etc. These species are also released directly into the atmosphere by very many plants and trees, and make a substantial contribution to global biogeochemical cycles. 

Aromatic groups are called aryl groups if they are attached directly to a parent structure. Common aryl groups are... 

Accordingly, phosphoric acid mono- and di-esters permit uncatalyzed glycosyl transfer from 0-(glycosyl)trichloroacetimidates (52a,55-57,58a,58b). The reaction is thus very useful in the synthesis of glycophos-pholipids (1,55), which are important constituents of cell membranes (1). Commonly, direct phosphorylation at the anomeric hydroxyl group leads to... 

The addition of water to a free carbocation intermediate of solvolysis can be distinguished from addition to an ion-pair intermediate by an examination of common ion inhibition of solvolysis. Common leaving group inhibition of solvolysis is observed when the leaving group ion (X ) acts, by mass action, to convert the free carbocation (R , Scheme 5A) to substrate (R-X). This results in a decrease in the steady-state concentration of R that leads directly to a decrease in the velocity of solvolysis. Some fraction of the solvolysis reaction products form by direct addition of solvent to the carbocation-anion pair intermediate. The external... 

Ortho and Para Directing Groups. In general the common rules of orientation regarding intermoleaular acylation can be extended to the... 

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