Carbonyl group geometry

In systems of proper geometry, nucleophiles within a side chain may be well connected for attack on ring atoms. For example, an aminomethyl group at the 5-position of a dibenzazepine-2-one was found to attack the carbonyl group (Section 5.16.3.5.2). Such reactions should be possible in rings of any size. 

Compare the geometries of triplet and ground state singlet anthrone. Where do they differ the most Focus on the carbonyl group. Has the CO bond distance altered Does the molecule incorporate a fully-developed CO n bond (as in ground state singlet anthrone), or a single bond (as in phenol) Is the carbonyl carbon planar or puckered Rationalize your observations. 

The most common reaction of aldehydes and ketones is the nucleophilic addition reaction, in which a nucleophile, Nu , adds to the electrophilic carbon of the carbonyl group. Since the nucleophile uses an electron pair to form a new bond to carbon, two electrons from the carbon-oxygen double bond must move toward the electronegative oxygen atom to give an alkoxide anion. The carbonyl carbon rehybridizes from sp2 to sp3 during the reaction, and the alkoxide ion product therefore has tetrahedral geometry. 

In pyridine- X-C interactions, the C - X moiety is roughly coplanar with the pyridine and the two C-N- X angles are approximately 120° [129,143, 144]. The same holds for other nitrogen heteroaromatics (e.g. pyrazine, quinoline, etc.) [145-147]. A carbonyl group pins the donors after a trigonal planar geometry and works either as a mono- [148,149] or bidentate XB acceptor [150]. Sulfoxides behave similarly [151,152] and imines form XB along the expected axis of the lone pair [153]. 

C-Alkylations of l,4-dihydro-27/-pyrazino[2,l-A]quinazoline-3,6-diones at positions C-l and CM were studied in detail. Compounds of type 57 could be alkylated diastereoselectively at C-l, owing to the geometry of the piperazine ring, which is locked in a flat boat conformation with the R4 or R1 substituent in a pseudoaxial position to avoid steric interaction with the nearly coplanar C(6)-carbonyl group. Alkylation of 57 (R2 = Me, Bn, R4 = Me) in the presence of lithium hexamethyldisilazide (LHMDS) with benzyl and allyl halides resulted, under kinetic control, in the 1,4-trans-diastereomer 59 as the major product, with retention of the stereocenter at CM (Scheme 5). 

X-ray structure analyses of Rh(COCH3)(I)2(dppp) (14) and [Rh(I I)(I)(//-I)(dppp)]2 (15), where dppp l,3-bis(diphenylphosphino) propane, were reported. Unsaturated complex (14) possesses a distorted five-coordinate geometry that is intermediate between sbp and tbp structures.69 Under CO pressure, the rhodium/ionic-iodide system catalyzes either the reductive carbonylation of methyl formate into acetaldehyde or its homologation into methyl acetate. By using labeled methyl formate (H13C02CH3) it was shown that the carbonyl group of acetaldehyde or methyl acetate does not result from that of methyl formate.70... 

In the ground state, aminomethylenemalonates possess an essentially planar geometry, which maximizes the electron delocalization in the molecules. In the heteropolar transition state, the plane of the groups R3 and NR R2 and the plane of the two carbonyl groups occupy orthogonal positions. More details of the dynamic and static stereochemistry of push-pull ethylenes, as in compounds 1 and 2, are discussed in two excellent reviews (73TS295 83TS83). 

It is evident from Figure 25 that the isoelectronic [Co4(CO)i2] also has a tetrahedral geometry,ld but the disposition of the carbonyl groups is different from that in [Fe4(CO)i3]2-. In fact, three are coplanar and doubly bridging the triangular Co3 base, whereas the remaining nine groups are terminal. 

The five iron atoms assume a square-pyramidal geometry the carbide atom has moved out of the basal plane by 0.18 A in the direction opposite to the apical iron atom. Two carbonyl groups in the basal plane are semi-bonding. 

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