A-C-atom

Shifts are also affected by steric compression of any kind on the atom nnder study. The effect on a C atom can... 

Electrophilic Attack at Carbon. Electiopliilic attack at a C-atom in pyiidines is paiticulaily difficult unless one oi mote strong... 

Lithium aluminum hydride reduction of 2,3,4-triphenylisoxazolin-5-one yielded 1,2,3-triphenylaziridine and dibenzylaniline. The reaction was considered to proceed by a concerted [l,3]-sigmatropic migration of the N to a C atom. HOMO-LUMO calculations show this type of concerted reaction is possible (Scheme 68) (80JA1372). 

The reversed polarity of the double bond is induced by a n electron-accepting substituent A (A = C=0, C=N, NO2) the carbon and proton in the p-position are deshielded (-A/effect, larger shifts). These substituents have analogous effects on the C atoms of aromatic and heteroaromatic rings. An electron donor D (see above) attached to the benzene ring deshields the (substituted) a-C atom (-/ effect). In contrast, in the ortho and para positions (or comparable positions in heteroaromatic rings) it causes a shielding +M effect, smaller H and C shifts), whereas the meta positions remain almost unaffected. 

Accordingly, the relaxation time of a C atom will increase the fewer hydrogen atoms it bonds to and the faster the motion of the molecule or molecular fragment in which it is located. From this, it can be deduced that the spin-lattice relaxation time of C nuclei provides information concerning four molecular characteristics ... 

Partial structure Protons Sh CH a C atoms one bond Sc separated by two or three bonds [ Sc Sc I... 

Figure 1 (a) Schematic representation of the electronic energy levels of a C atom and... 

The key study for our development of molecular mechanics was that by Scbachtschneider and Snyder (1969), who showed that transferable force constants can be obtained provided that a few off-diagonal terms are not neglected. These authors found that olf-diagonal terms are usually largest when neighbouring atoms are involved. A final point for consideration is that the C atom in OCS is obviously chemically different from a C atom in ethane and from a C atom in ethyne. It is necessary to take account of the chemical environment of a given atom. 

The reaction described here is probably responsible for the slow decomposition of many oxaziranes at room temperature, 2-fert-Alkyl-oxaziranes are stable at room temperature for unlimited periods radical attack on the a-C-atom of the iV-alkyl group is not possible. By contrast, oxaziranes containing a C—H group which is alpha to the N-atom are unstable at room temperature on keeping they are largely decomposed within a few weeks. 

From ESR studies the formation of free radicals on the a-C atom of the amines attached to hydroxyalky group as ... 

Trisubstituted paraffins. A trisubstituted paraffin with three different substituents Y, T, Z (none of which can be an alkyl radical) has the molecular formula C Hj. XYZ. The structure formula is a tree. Examine the three linking paths YY, YZ, and ZX. It is easy to see that there exists one and only one point which is common to all three paths, a vertex of degree 4 (a C-atom) we call it "traffic center" of the tree, point V for short (F for "Verkehrszentrum"). 

We start with the point F, which corresponds to the factor x (a C-atom). Next, F is connected to Y by a path which contains m carbon atoms which are capped by a pair of alkyl radicals, w 0, 1,2,. ... This construction produces the factor (3.15), as we have seen in the previous section. 

The second electron, shown in blue, is contributed by another atom. This could be another H atom in H2l an F atom in HF, a C atom in CH4, and so on. 

SOLUTION For simplicity, we show only the carbon atoms there is an H atom attached to each bond extending from a C atom. 

Self-Test 18.6B In an alcohol, an —OH group is attached to a C atom. Which of the following alcohols is chiral (a) CH3CH2OH (b) CH3CH(OH)CH3 ... 

In the same manner, the rc-electron densities of the monomer and the cation are affected. Substituents, which decrease the electron density at the P-C-atom, that is, the place of the primary attack on the double bond, increase the positive charge at the a-C-atom of the cation and therefore its electrostatic interaction with a negative reaction centre (qa(cation) = —2.08 + 2.53qp(monomer) r = 0.93 n = 13). The previous equation shows that the electron density of the cation is more influenced than that of the monomer (Aqp(monomer) = 0.1 and Aqjcation) = 0.25).. 

The color hues produced in the reaction do not appear to be affected by differing substituents at the amine nitrogen however electron-attracting substituents at the a-C atom appear to reduce the detection sensitivity of the reaction [1]. The colors produced remain stable for months in the dark. In the light the zones produced by primary amines fade more rapidly than those from secondary amines [1]. 

Using mass spectrometers, scientists have determined that the mass of a C atom is 1.992646 X 10 g This experimental mass combined with the definition of the mole gives the number of atoms in one mole ... 

C 1 O /s the only molecule in which a C atom has fewer than four bonds. 

The amine opens the THF ring system because of a nucleophilic attack at the a-C atom of the coordinated THF. Owing to the movement of a proton from the ethyl to the amide group with simultaneous ethene elimination, a betaine structure appears. 

Acylierung des a-C-Atoms der Aminosaure, der eine Decarboxylierung vorangeht oder folgt. 

The compounds [Fe(C5Me4SCMe3)2][M(mnt)2] (M = Ni, Pt) are the only cases of salts based on metallocenium derivatives and on [M(mnt)2 complexes where the crystal structure is based in parallel arrangements of the type I chain motif [49]. In the chains the [Pt(mnt)2]- units are considerably tilted in relation to the chain direction, and short interatomic D+A- intrachain contacts were observed, involving one C from the Cp and a S atom from the anion, with a C-S distance of the order of dtf/. Relatively short interchain interionic distances were observed, where the closest corresponds to a S... C, involving one S atom from the anion and a C atom from a Me group of the cation, exceeding dw by 10%. 

The reactions of dichlorocarbene with phosphorus ylides result in the corresponding olefins and phosphines.66-68 In the reaction of dichlorocarbene generated in situ with tributyl- and triphenylmethylenephosphoranes or triphenylethylidenephosphorane, the olefin yield increases as the nucleo-philicity of phosphorus ylide increases. According to,67 the reaction starts from the electrophilic attack of carbene at the a-C atom of phosphorus ylide. Then the intermediately formed betaine (28) (Scheme 14) decomposes to eliminate the phosphine molecule and form dichloroolefin (29). 

The comparison of the BDE of hydrocarbons and amines proves the strong effect of the amino group on the BDE of the a-C—H bond. This is the result of the strong interaction of the a-C atom free valence of the aminoalkyl substituent with the p-electron pair of nitrogen atom. The energy of such interaction demonstrates the difference in the BDE of the a-C—H bond in hydrocarbons and amines (AD = Dc h(RCH3) — Dc H (RNH2)). 

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