Carbon atoms carbinol

We can begin with either a carbon or a proton resonance and obtain equivalent results. We will use the carbon axis as our starting point because we usually have less overlap there. For example, a line drawn parallel to the proton axis at about 68 ppm on the carbon axis (the carbinol carbon) intersects five cross peaks none of the five correlations corresponds to the attached proton (VCH) at 3.8 ppm. Four of the cross peaks correspond to the two pairs of diastereotopic methylene groups (2.48, 2.22,1.45, and 1.28 ppm) and these represent, 2iCH, or two-bond couplings. The fifth interaction (3/CH) correlates this carbon atom (68 ppm) to the isopropyl methine proton (1.82 ppm), which is bonded to a carbon atom in the /3-position. The other carbon atom in a /3-position has no attached protons so we do not have a correlation to it from the carbinol carbon atom. Thus, we have indirect carbon connectivities to two a-carbons and to one of two /3-carbons. 

Cyanogen bromide reacts with threo- 2-piperidyl carbinol (278) to form the trans imine (279). The latter is also formed from the erythro 1-carbamate (280) using thionyl chloride for the cyclodehydration reaction. The latter reaction therefore proceeds by inversion of the configuration at the carbinol carbon atom (73AP284). 

One way of organizing the alcohol family is to classify each alcohol according to the type of carbinol carbon atom the one bonded to the —OH group. If this carbon atom is primary (bonded to one other carbon atom), the compound is a primary alcohol. A secondary alcohol has the —OH group attached to a secondary carbon atom, and a tertiary alcohol has it bonded to a tertiary carbon. When we studied alkyl halides (Chapter 6), we saw that primary, secondary, and tertiary halides react differently. The same is hue for alcohols. We need to learn how these classes of alcohols are similar and under what conditions they react differently. Figure 10-2 shows examples of primary, secondary, and tertiary alcohols. 

A secondary alcohol has two groups on the carbinol carbon atom. Consider two possible reactions, with either group added as the Grignard reagent. 

A ketone has two alkyl groups bonded to its carbonyl carbon atom. Addition of a Grignard reagent, followed by protonation, gives a tertiary alcohol, with three alkyl groups bonded to the carbinol carbon atom. 

The first step forms an intermediate in which the alcohol oxygen replaces one of the oxidant s original bonds to oxygen. In the next step, a base (often water or other solvent) removes a proton from the carbinol carbon atom, giving it a double bond to oxygen, which... 

Oxidation of tertiary alcohols is not an important reaction in organic chemistry. Tertiary alcohols have no hydrogen atoms on the carbinol carbon atom, so oxidation must take place by breaking carbon-carbon bonds. These oxidations require severe conditions and result in mixtures of products. 

In addition to losing water, alcohols commonly fragment next to the carbinol carbon atom to give a resonance-stabilized carbocation. This fragmentation is called an alpha cleavage because it breaks the bond next to the carbon bearing the hydroxyl group. 

The anions of Reissert compounds 19 and 20 undergo reaction with aldehydes to form esters of secondary alcohols containing the 2-quinolyl or 1-isoquinolyl group bonded to the carbinol carbon atom. Thus benzaldehyde, l-benzoyl-l,2-dihydroquinaldonitrile (7), and phenyllithium in ether-dioxan at — 10° gave 29, and benzaldehyde, 2-benzoyl-l,2-dihydroisoquinaldonitrile (8), and phenyllithium in ether-dioxan at —10° (or sodium hydride in refluxing... 

An alternative suggestion [30,36] involves rate-determining replacement of hydrogen on the hydroxyl-bearing carbon by bromine, followed by loss of HBr (Fig. 13a). It seems more reasonable to regard the key step as the removal of a hydride ion from the carbinol carbon atom (Fig. 13b), perhaps concerted with the loss of the hydroxylic proton to the solvent. Certain ethers are readily oxidised to carbonyl compounds by a process of this kind [36b]. Present evidence, however, does not permit... 

Primary and secondary alcohols appear to oxidize rapidly to the corresponding carbonyl compounds with good efficiencies [10]. The initial point of attack is predominantly on the hydrogen on the carbinol carbon atom. Tertiary alcohols do not have a hydrogen in this position and are relatively resistant to oxidation. Alcohols, like aldehydes, are usually important intermediates in paraffin oxidations [18]. They undergo subsequent oxidation somewhat less readily than aldehydes, but primary and secondary alcohols oxidize much faster than the starting paraffin(s). Quite unlike aldehydes, however, alcohols do not, in general, autoxidize readily by themselves. Moreover, the deliberate addition of alcohol to an oxidation can slow or even stop the reaction [10, 19-21]. 

N. Kornblum and L. Fishbein,/. Amer. Chem. Soc., 77, 6266 (1955) F. G. Bord-well and R. L. Arnold, J. Org. Chem., 27, 4426 (1962). An acidic medium suppresses formation of the nitronate ion that is an intermediate in epimerization, not only at the nitro carbon center but also at adjacent carbinol carbon atoms. 

Chart L Determination of absolute configuration using mandelate esters. Con-figurations denoted refer only to carbinol carbon atom. Key A, Ref, 7 B, Ref, 8 C, Ref. 9 D, Ref. 10 and E, Ref. 5. Continued on next page. 

Chart I, Continued. Determination of absolute configuration using mandelate esters. Configurations denoted refer only to carbinol carbon atom. Key see... 

The measurement of chemical shifts in alicyclic hydrocarbons also provides information regarding the conformational preference of substituted rings. The chemical shifts of the carbinol carbon atom... 

One way of organizing the alcohol family is to classify each alcohol according to the type of carbinol carbon atom the one bonded to the —OH group. If this carbon atom is primary (bonded to one other carbon atom), the compound is a primary alcohol. A secondary alcohol has the — OH group attached to a secondary carbon atom, and a... 

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