Carbon valency

If 90 is added to the designated R number, the resulting single digits individually reflect, in sequential order, the number of carbon, hydrogen, and fluorine atoms present, respectively. Chlorine is deterrnined by difference, ie, the carbon valency of 4 minus number of H and F atoms. For example, R-12 12 + 90 = 102, indicating 1 carbon, 0 hydrogen, 2 fluorine, and 2 chlorine atoms by difference. 

The C—S bond lengths vary upon changing carbon valence states. However, the sulfones and sulfoxides show less sensitivity to these changes than the analogous sulfides . These effects can be illustrated by considering the C—S bond lengths (A) in analogous dimethyl and diphenyl derivatives ... 

In each of these hydrocarbons we also see a C—H bonding charge concentration with a maximum in the carbon valence shell corresponding to the C—H bonding domain, and... 

Walsh, A. D. Discussions Faraday Soc. 2, 18 (1947) Walsh stated the following rule if a group X attached to carbon is replaced by a more electronegative gTOup Y, the carbon valency toward Y has more p character than it had toward X. For a review, see Bent, H. A. Chem. Revs. 61, 275 (1961)... 

The benzene molecule is a remarkable structure with six carbons in a hexagonal ring. To satisfy the carbon valence of four, every other carbon-to-... 

The added hydrogen forms saturated molecules where all single-carbon valence bonds become satisfied or attached to other atoms, thus producing solid saturated or trans fatty acids that may increase LDL cholesterol (the bad cholesterol) attributed to numerous health risks. 

You re now finished with the simple part. One carbon atom in the structure still requires two additional electrons to fill its valence shell. The only way to fill this shell is to take the lone pair of electrons you added to one of the carbons and instead use it to create a double bond between two of the carbons. You then need to move the hydrogens around to ensure that each carbon has a total of four bonds. Only one arrangement of hydrogen atoms to the three carbons allows you to fill all the carbon valence shells, as you can see in the following figure ... 

Read from right to left. b Suffix B = bromine prefix C - cyelo. c Number of fluorine atoms. d Number of hydrogen atoms plus one. c Number of carbon atoms minus one (omit if 0). f That is, discrepancy with a carbon valency of four after allowance for bromine... 

For convenience, paraffinic rings often are represented by simple geometric figures as shown below. Each comer of a figure represents a carbon atom, and the carbon valence of four is satisfied with hydrogen atoms which are not shown. ... 

The degree of shielding of the proton by the carbon valence electrons depends on the character of the substituent atoms and groups present, and particularly on their electron-attracting power, or electronegativity. For a grouping of the... 

If the carbon valence angles are kept near the tetrahedral value, you will find that you can construct ball-and-stick models of the cyclohexane six-carbon ring with two quite different conformations. These are known as the chair and boat conformations (Figure 12-3). It has not been possible... 

The product of a elimination is a neutral species that resembles a carbocation in having only six carbon valence electrons. The simplest carbene is CH2, methylene. Carbenes are highly reactive, so much so that they cannot be isolated. Their involvement in reactions usually has to be inferred from the nature of the products or the reaction kinetics. The characteristic carbene reactions involve forming an electron-pair bond to the carbene carbon by reacting with cr bonds, it bonds, or unshared pairs ( ), Some of these reactions are illustrated here for methylene ( CH2). ... 

We could simply proceed to inspect these orbitals to see which overlap with each other, and then begin to make molecular orbitals in the way described in the previous section. Unfortunately, the situation is now quite complicated. The hydrogen number 1 interacts with allfour of the carbon valence orbitals. 

The classical valency concept of the tetrahedral carbon atom has been more than fully verified by its success in explaining the chemistry of countless thousands of organic compounds. The first direct physical confirmation of the tetrahedral distribution of carbon valency bonds, however, came with the elucidation of the structure of diamond by W. H. and W. L. Bragg (1913) using the newly discovered method of X-ray diffraction. 

The distances between the centers of oxygen atoms of hydroxyl groups located at different projected angles are given in Table I. In calculating these distances tetrahedral angles were employed for the carbon valences carbon-carbon and carbon-oxygen bond distances of 1.54 and 1.45 A. respectively, were accepted.10... 

In such representations the convention is to assume a carbon atom at each apex of the ring and that the carbon valency of 4 is made up by the appropriate number of hydrogen atoms, which are not shown explicitly A similar convention is used to simplify the writing of the structure of noncyclic compounds as well, as illustrated in some of the examples below. 

Figure 8. S-C and Se-C bond lengths in sulfides and selenides with various carbon valence states (after [48]).

One of the celebrated successes of orbital hybridization is the elucidation of multiple bonding, which stems from the Lewis formulation of a chemical bond as a shared electron pair. In a compound such as ethylene the saturation of the carbon valence shells can only be achieved by the sharing of two electron pairs between the two carbon atoms. 

Intramolecular forces must dominate the correlation, and this notion provides the basis for a theoretical discussion of g,--values. Intermolecular forces may be taken into account as a secondary perturbation. An important case concerns the arrangement of segmental dipoles, aligned perpendicularly with respect to the chain contour, along a polymeric molecule which has a backbone of carbon atoms. Part of the dipolar correlation is fixed, of course, by the tetrahedral nature of the carbon valence, but part depends on the possible rotation about the C-C bonds of the chain. For completely free rotation it may be shown that gT = 11/12. 

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