The microwave spectra of four isotopic species of chlorine azide, ClN3, have been observed in the frequency range 26–48 GHz. From the measured values of the rotational constants, the molecule has been deduced to be planar with the following internuclear parameters: r(Cl–N(1)) = 1.745 ± 0.005 A, r(N(1)–N(2)) = 1.252 ± 0.010 A, r(N(2)–N(3)) = 1.133 ± 0.010 A, ∠ClN(1)N(2) = 108°40′ ± 30′, ∠N(1)N(2)N(3) = 171°56′ ± 30′, with Cl and N(3) trans. Values for the chlorine quadrupole coupling constants were obtained for all isotopic species, and for the most abundant, 35Cl14N3, were transformed into the principal field gradient axis system. The values obtained are consistent with the deduced structure.

Microwave Spectrum and Structure of Chlorine Azide

Halogen pure electrical quadrupole resonance frequencies have been measured in the three 1:1 complexes, CBr4·p‐xylene, CCl4·p‐xylene, and Br2·benzene. From an examination of the measured frequencies of the complexes and the halogen‐containing compounds (CBr, CCl4, and Br2) together with information from the x‐ray structure determinations for two of the complexes, it has been concluded that little if any charge transfer exists in the ground state of these complexes.

Lack of Charge Transfer in Aromatic Charge—Transfer Complexes

The 35Cl NQR frequencies (at 77°K) of a number of chlorobenzene derivatives have been measured. The frequencies (including additional data from the literature) have been correlated with characteristic parameters, such as Taft's σI and σR. It is found that the Bray–Barnes relation can be somewhat improved by introducing a parameter κ: ν = ν0 +  ∑ iκi. The following relations are found: (a) the effects of more than one substituent on the benzene are additive; (b) steric effects (o‐substituents) are not important for the NQR frequencies; (c) a correlation between the NQR frequency ν and Taft's σI and σR (correlation coefficient r = 0.976) shows the importance of the inductive effect on NQR. The mesomeric effect plays only a minor role in 35Cl NQR in benzene derivatives. Unknown σI values may be gained from NQR measurements; for the evaluation of σR, the determination of the chemical shift of 19F NMR seems to be the better method.

Correlations between 35Cl Nuclear Quadrupole Resonance (NQR) Frequencies of Chlorobenzene Derivatives and Characteristic Reaction Parameters of the Substituents

Publisher Summary The Hammett equation is one of the most widely applied relations between the structure and reactivity of organic compounds. This equation relates the relative reactivities of the series of di- and poly-substituted benzene derivatives. The various applications of the Hemmett equation to the reactions of heterocyclic compounds are discussed. Some of the particular situations arising in the heterocyclic aromatic chemistry, which can be treated in terms of the Hammett equation, include (1) reactivity of the groups attached to a heteroatom, (2) transmission through a heterocyclic ring, both six- and five-membered, and (3) fused ring systems. The transmission of the effects of one substituent in a disubstituted heterocycle is presented. The chapter also discusses the application of the Hammett equation to (1) bicyclic aromatic compounds of the quinoline and isoquinoline type, and (2) heterocycles of the indole-benzofuran type.

Applications of the Hammett Equation to Heterocyclic Compounds

The microwave spectra of CH3C35Cl:CH2 and CH3C37Cl:CH2 have been observed in the ground and first excited torsional states. The ground‐state rotational constants of CH3C35Cl:CH2 are A=9272.79±0.10 Mc/sec, B=4983.84±0.10 Mc/sec, and C=3304.39±0.10 Mc/sec. The ground‐state rotational constants for CH3C37Cl:CH2 are A=9272.31±0.10 Mc/sec, B=4850.48±0.10 Mc/sec, and C=3245.11±0.10 Mc/sec. The quadrupole coupling constants along the appropriate principal inertial axes in the ground torsional state of CH3C35Cl:CH2 are χaa=−68.15±0.10 Mc/sec, χbb=37.11±0.10 Mc/sec, and χcc=31.04±0.10 Mc/sec. The quadrupole coupling constants for CH3C35Cl:CH2 in the excited torsional state were within the experimental error of the corresponding ground‐state values. The quadrupole coupling constants in CH3C37Cl:CH2 are χaa=−53.80±0.10 Mc/sec, χbb=29.30±0.10 Mc/sec, and χcc=24.50±0.10 Mc/sec. Analysis of the first excited‐torsional‐state rotational spectrum yielded a barrier to the internal rotation of the methyl group of 2671±20 ca...

Barrier Studies in the Halopropenes. I. The Microwave Spectrum, Barrier to Internal Rotation, Quadrupole Coupling Constants, and Microwave Double‐Resonance Spectra of 2‐Chloropropene

Induction studies have been carried out in several groups of halogen‐containing organic compounds by means of the halogen pure quadrupole spectra In several straight‐chain compounds inductive effects have been examined as a function of the length of the chain in some monohalogenated‐paraffin hydrocarbons and as a function of the number of carbon atoms separating halogen atoms attached to either end of dihalogenated‐paraffin hydrocarbons The effects of the hybridization of the carbon atom have also been examined in some aliphatic hydrocarbons Chlorine pure quadrupole resonance frequencies from chlorine atoms bonded to atoms other than carbon, such as silicon, nitrogen, and sulfur, have been measured, and the effects of these different atoms upon the Cl35 resonance frequencies are qualitatively discussedInductive effects have also been examined in different groups of aromatic compounds The inductive effect in several chlorobenzyl compounds is found to be about ¾ of what it is in the corresponding chlorobenzene compounds as determined from a comparison of the Cl35 resonance frequencies Definite discrepancies have been observed between the Cl35 spectra obtained from several aromatic compounds which have molecular structures similar to anthraquinone and the Cl35 frequencies that can be predicted from data obtained from chlorobenzene compounds and Hammett σ valuesEmploying the linear relationship between Cl35 resonance frequency and Hammett σ values, several Cl35 frequencies were predicted and compared to the measured frequencies in some chlorobenzene compounds Some unknown σ values have also been predicted A linear relationship between Br81 resonance frequencies and Hammett σ values has been developed from measured bromine quadrupole frequencies Several halogen frequencies from some unrelated compounds have been measured and are tabulated in this paper

P. J. Bray

Papers

Induction Studies in Several Groups of Halogen‐Containing Organic Compounds by Their Cl35, Br79, or Br81 Pure Quadrupole Resonance Spectra