Carbonyl group defined

FIGURE 13.8 The Johnson picture of fluxionality. A close-packed cuboctahedron of carbonyl groups defines a cavity in which the triangle of metals fits. This triangle can rotate within a fixed set of CO groups. 

Several of the functional groups listed in Table 25.4 contain a C=O double bond. This particular group of atoms is called a carbonyl group. The carbonyl group, together with the atoms that are attached to the carbon of the carbonyl group, defines several important functional groups that we consider in this section. 

The basic carbohydrate molecule possesses an aldehyde or ketone group and a hydroxyl group on every carbon atom except the one involved in the carbonyl group. As a result, carbohydrates are defined as aldehyde or ketone derivatives of polyhydroxy alcohols and their reaction products. A look at the formula for glucose shows that it contains hydrogen and oxygen atoms in the ratio in which they are found in water. The name carbohydrate... 

If there is a carbonyl group in the branch (or a terminal COOH or its equivalent), its position (assigned lowest number when stereochemistry is being considered) is used to define the configurational prefix (see examples 1 and 3 in Chart V). Use of the R,S system is generally preferred, as less open to misinterpretation. 

The group A may be regarded as a structural equivalent for the carbonyl group B, since introduction of A into a molecule is actually an indirect means of introducing B. It is convenient to have a word for units within molecules such a word is synthon, introduced by Corey, which is defined as a structural unit within a molecule that can be formed and/or assembled by known or conceivable synthetic operations. There are many other synthons equivalent to A and B, for example, C (by Reactions 16-23 and 19-3) and D (by Reactions 10-2 and 16-22). ... 

This section deals with reactions that correspond to Pathway C, defined earlier (p. 64), that lead to formation of alkenes. The reactions discussed include those of phosphorus-stabilized nucleophiles (Wittig and related reactions), a a-silyl (Peterson reaction) and a-sulfonyl (Julia olefination) with aldehydes and ketones. These important rections can be used to convert a carbonyl group to an alkene by reaction with a carbon nucleophile. In each case, the addition step is followed by an elimination. 

A second reason why AI is of value to scientists is that it offers powerful tools to cope with complexity. In favorable circumstances, the solutions to problems can be expressed by rules or by a well-defined, possibly trivial, model. If we want to know whether a compound contains a carbonyl group, we could record its infrared spectrum and check for a peak near 1760 cm1. The spectrum, paired with the rule that ketones generally show an absorption in this region, is all that we need. But other correlations are more difficult to express by rules or parametrically. What makes a good wine We may (or may not) be able to recognize a superior wine by its taste, but would have considerable difficulty in determining whether a wine is good, or even if it is palatable, if all we had to go on was a list of the chemicals of which it is comprised. 

The [2+2]-photocycloaddition of carbonyl groups with olefins (Paterno-Buchi reaction) is one of the oldest known photochemical reactions and has become increasingly important for the synthesis of complex molecules. Existing reviews have summarized the mechanistic considerations and defined the scope and limitations of this photocycloaddition73. Although this reaction likely proceeds via initial excitation of the carbonyl compound and not the excited state of the diene, the many examples of this reaction in natural product synthesis justify inclusion in this chapter. 

Base removes a proton from adjacent to a carbonyl group. We can use a general to represent the base however, we could use hydroxide, since that is released upon dissolving sodium carbonate in water. It does not matter which a-position we choose they are actually all equivalent in this symmetrical substrate. The nucleophilic attack of the enolate anion onto the second carbonyl is followed by base-initiated dehydration, so that a favourable conjugated ketone is the product. As you can see, the size of the ring systems is automatically defined by the reaction. 

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