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1. Calculations were made of the constants occurring in semiempirical equations expressing the relation of interatomic distances to theπ -electron charges of bonds in organic compounds. 2. It was shown that in the case of C-C bonds changes inσ -electron charge have relatively little effect on interatomic distances. 3. It was noted that a nitrogen atom can act as a donor of threeπ -electrons.

A dependence was shown to exist between the electronic charges and the lengths of σ -bonds of a saturated carbon atom, which permitted us to explain and to correct the existing data on interatomic distances.

1. Covalent bonds in molecules are formed byσ- andπ-electron charges, which are not in general equal to a whole number of electrons. 2. All bonds attached to atom donors ofπ-electrons haveπ-electron charges. 3. To the approximation, a linear relationship can be assumed betweenπ-electron charge and bond length. 4. A new and very promoting line of work is being developed in the theory of the electronic structure of molecules.

1. A scheme according to which the electronegativities of the halogens were calculated from the dipole moments of halomethanes was substantiated, and a low value of the electronegativity of fluorine, xF= 2.79, was obtained. In particular, the introduction of a high electronegativity of fluorine, xF=3.5, into this scheme does not lead to satisfactory results. 2. The eleetronegativity of fluorine, xF=2.92, was calculated according to data on the dipole moments of fluorosilanes. 3. In a calculation of the electronegativity of fluorine according to thermochemical data, an approximate consideration of the partial double-bonded character of the “single” bond lowers the value of xF to 2.65–2.9. 4. We must reckon not only with the possibility of different electronegativities of fluorine in principle, but also concretely with its low value xF ≈ 2.8.

1. The lengths of C-H bonds in allene and ethylene and of C-C bonds in ethylene were calculated. 2. The π -electron charges of C-C bonds in anthracene, triphenylene, and ovalene were calculated. A comparison was made with Scherr's calculations. 3. It was shown that, when a nitrogen atom forms a bond with an atom-donor ofπ -electrons, the free pair of electrons almost always passes, wholly or partially, into the bond and increases itsπ -electron charge. 4. A table is given of π -electron charges in organic compounds. 5. A discussion is given of various hypotheses which have been advanced for the explanation of the regularities observed in interatomic distances.

1. Simple semiempirical equations are proposed for the relation between force constants and characteristic frequencies of bonds on the one hand and total (σ- + π-) electronic charges of bonds on the other. These equations are checked by calculation of the total electronic charges of ethylene and acetylene. The electronegativity of acetylenic carbon is determined. 2. It is shown that it is possible to calculate π-electronic charges of bonds by two methods which give closely agreeing results-from bond lengths and from electronegativities. 3. An additive scheme is proposed for the calculation of heats of formation of unsaturated hydrocarbons from their elements; the scheme is analogous to that already proposed for saturated hydrocarbons. The separate π-electronic energies of C-C and C-H bonds are calculated. Electronegativities are calculated for carbon atoms in the α- and β -positions with respect to the acetylenic bond of normal 1-alkynes. 4. It is shown that dipole moments of polyatomic molec,,les are generally determined by the nonintegral character of the electronic charges of individual bonds. It is possible to estimate electronegativities of atoms from from dipole moments.

1. It was shown that there is a relation between the thermodynamic (energy) and kinetic factors of chemical reactions, on the one hand, and the electron charges of bonds in the reactant molecules, on the other. Three theses were formulated, and it was shown that from these theses we can derive rules, found earlier by empirical methods, for the direction of organic reactions and also regularities observed in the metallation of hydrocarbons and in certain atomic and free-radical exchange. reactions.It was shown that there is a relation between activation energies and electron charges of bonds. 2. A new qualitative interpretation of the mechanism of the mutual effects of atoms was illustrated by the examples of acetic and chloroacetic acids.In the course of these considerations it was suggested that the directional variation of the electronegativity of an atom is the cause of the trans effect.

1. Theπ-electron distribution hypothesis has been extended to organic compounds containing the CCl, C8r, Cl, Co, Cn, NN and NO bonds. 2. The reliability of the basic data and the final calculated results forπ-electron changes of bonds are discussed.

On the basis of the fact that the electronic shielding of the protons should be related to the value of the electronic charge at the corresponding C-H bond, the chemical shifts in the PMR spectra were compared with the electronic charges of the σ-bonds of CH in alkanes and cycloalkanes. In this case, the variation of the chemical shifts in structurally different bonds of saturated hydrocarbons and the unusual chemical shift of the protons of cyclopropane were explained.

1. The author proposes to construct an electronic theory of the mutual effects of atoms in organic compounds on the basis of the concept of the electronic charge of a bond, which in the general case is not equal to a whole number of electrons. 2. An equation is proposed which expresses the dependence of electronic charges of bonds on the electronegativities of the atoms. An equation is derived for the calculation of heats of formation of gaseous saturated hydrocarbons from their elements with the aid of values of electronic charges of bonds calculated by the first equation. The agreement found between the experimental values of heats of formation and values calculated with these equations confirms the theoretical postulates on which they were based. In particular, confirmation is found for the postulate that the energies of the σ-bonds are, to the first approximation, directly proportional to their σ-electron charges. A new additive scheme is proposed for the calculation of heats of formation of saturated hydrocarbons. In this scheme the terms of the summation are products of σ-electron charges of bonds and specific electronic energies.

The previously proposed explanation for the variation in the lengths ofσ-bonds of organic molecules within the framework of the theory of electronic charges of the bonds is confirmed by the newest data on the interatomic distances and can be used for a quantitative treatment of the Lide effect.

The electronic charges of bonds in acetylene were calculated from thermochemical data with results that are in satisfactory agreement with the results of two other calculations. A new proof was found of the localization of a π -electronic cloud amounting to 0.7–0.8 electron on the C-H bond in acetylene.

1. The energy of the C-H bond in methane is about 64 kcal and is. in accord with the position of carbon in the periodic system. 2. The heat of atomization of carbon into atoms that preserve their valence state is. approximately 32 kcal/g-atom.

1. It was shown that a linear relationship exists between the frequencies of valence vibrations and electronic charges of C-H bonds in simple hydrocarbons of various classes. 2. Three different methods of calculating the electronic charges of bonds in acetylene give very similar results.

1. A linear relationship has been obtained between the integral intensity of the IR absorption band corresponding to valence vibrations, and the electronic charges of the bonds. This relationship is obeyed for vibrations of similar mode and frequency. 2. For the methyl halides CH3X and CD3X (X=CI, Br, I) and the alkyl groups CH3, CH2, and CH a linear dependence was found between the square root of the intensity and the electronic charge of the CH or CD bond.