Alcohols substituent groups

The triaLkoxy(aryloxy)boranes are typically monomeric, soluble in most organic solvents, and dissolve in water with hydrolysis to form boric acid and the corresponding alcohol and phenol. Although the rate of hydrolysis is usually very fast, it is dependent on the bulk of the alkyl or aryl substituent groups bonded to the boron atom. Secondary and tertiary alkyl esters are generally more stable than the primary alkyl esters. The boron atom in these compounds is in a trigonal coplanar state with bond hybridization. A vacantp orbital exists along the threefold axis perpendicular to the BO plane. 

Compounds with a smaller/C., and larger pKa are less acidic, whereas compounds with a larger/Ca and smaller plsimple alcohols like methanol and ethanol are about as acidic as water but substituent groups can have a significant effect, tert-Butyl alcohol is a weaker acid, for instance, and 2,2,2-trifluoroethanol is stronger. Phenols and thiols, the sulfur analogs of alcohols, are substantially more acidic than water. 

When a carbonyl group is bonded to a substituent group that can potentially depart as a Lewis base, addition of a nucleophile to the carbonyl carbon leads to elimination and the regeneration of a carbon-oxygen double bond. Esters undergo hydrolysis with alkali hydroxides to form alkali metal salts of carboxylic acids and alcohols. Amides undergo hydrolysis with mineral acids to form carboxylic acids and amine salts. Carbamates undergo alkaline hydrolysis to form amines, carbon dioxide, and alcohols. 

Substituents replacing the hydrogen atom of an alcoholic hydroxy group of a saccharide or saccharide derivative are denoted as O-substituents. The 0- locant is not repeated for multiple replacements by the same atom or group. Number locants are used as necessary to specify the positions of substituents they are not required for compounds fully substituted by identical groups. Alternative periphrase names for esters, ethers, etc. may be useful for indexing purposes. For cyclic acetals see 2-Carb-28. 

A molecule of aliphatic ester possesses two substituents around the ester group —C(0)0—, namely, alcohol and acid residues. Ester group decreases the BDE of a-C—H bonds in both substituents alcoholic and acidic. Therefore, an ester molecule has two different types of weak C—H bonds that are attacked by peroxyl radicals a-C—H bonds of the alcohol substituent —CH20C(0)R and the a-C—H bonds of the acid substituent —CH2C(0)0R. The values of BDE of these types of C—H bonds are close but not the same. The values of BDE of the C—H bonds are collected in Table 9.10. 

Conformational analysis reveals that the ester of type RCOOR (47) adopts a planar conformation in which CO and OR groups are cisoid and the two carbonyl groups antiparallel, as shown in 47 (Scheme 1-13). Three conformations for the alcohol substituents might be considered (49-51). Examination of the attacking mode of the reagent suggests that 49 and 50, the favorable... 

When coordinated to metal ions in their normal or higher oxidation states, an isocyanide is rendered susceptible to attack at the ligating carbon atom by nucleophilic reagents.1 When alcohols or amines are the nucleophiles, carbene complexes that may be prepared for a variety of metals and substituent groups are obtained. The first fully characterized compounds were of platinum(H),2 and general methods of their preparation, with particular examples, are given below. 

Problem 16.39 Use the mechanism of esterification to explain the lower rates of both esterification and hydrolysis of esters when the alcohol, the acid, or both have branched substituent groups. -e... 

The usefulness of direct ester formation from alcohols and acids is limited to those alcohols or acids that do not undergo extensive side reactions in the presence of strong acids. Furthermore, if the alcohol is particularly bulky the reaction usually will not proceed satisfactorily because the intermediates 7 and 8 (as well as the product) are rendered unstable by crowding of the substituent groups. 

This addition is sensitive to steric biases in the olefin, and the methylene group will enter from the least hindered side of the molecule. Alcohol substituents in the olefin will facilitate the reaction and guide the methylene group syn to fire alcohol. 

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