Richard B. Bernstein

Isotope Effect in Continuous Ultraviolet Absorption Spectra: Methyl Bromide‐d3 and Chloroform‐d

A comparison of the continuous ultraviolet absorption spectra of CH3Br and CD3Br indicated a nearly constant shift of +280±50 cm—1 upon deuterium substitution. In the case of CHCl3 and CDCl3 the shift was less than the uncertainty of ±50 cm—1. These results are interpreted in terms of the Herzberg‐Goodeve picture involving the carbon‐halogen bond rupture.The ultraviolet absorption spectra of CCl4, CFCl3, CH2Cl2, CF2Cl2, and CHFCl2 are also reported.

Substituted Methanes. XXVI. Raman and Infrared Spectral Data, Assignments, Potential Constants, and Thermodynamic Properties for CHBrCl2 and CDBrCl2

Raman displacements, semiquantitative relative intensities, and quantitative depolarization factors for liquid bromodichloromethane and deuterobromodichloromethane, as well as infrared wave numbers and percent transmission curves for both the liquid and gas in the region 400—4000K (K = kaysers = cm—1), were obtained and compared with previous data. Assignments were made for both molecules and a reasonable set of potential constants was determined by use of Wilsons FG matrix method. The heat content, free energy, entropy, and heat capacity were calculated for 12 temperatures from 100° to 1000°K.

Substituted Methanes. XVII.* Vibrational Spectra, Potential Constants, and Calculated Thermodynamic Properties of Diiodomethane

Raman displacements, semiquantitative relative intensities, quantitative depolarization factors, and wave numbers for the infrared bands in the region 400–3800 cm−1 have been obtained for liquid CH2I2. A normal coordinate treatment was carried out, and a reasonable set of potential constants was determined, using the most general quadratic potential energy function. Assignments were made for all observed Raman and infrared bands. The heat content, free energy, entropy, and heat capacity at constant pressure were calculated for 12 temperatures from 100° to 1000°K.

Substituted Methanes. XVI. Vibrational Spectra, Potential Constants, and Calculated Thermodynamic Properties of Dibromodifluoromethane

Raman displacements, semiquantitative relative intensities, and quantitative depolarization factors of liquid CBr2F2, and infrared wave numbers and the percent transmission in the region 450–4000 cm−1 for gaseous CBr2F2 have been obtained. Satisfactory assignments were made for all the observed bands. Using the Wilson FG matrix method, with a potential function containing all possible second‐degree terms, reasonable values of the potential constants were calculated. Finally, the heat content, free energy, entropy, and heat capacity for the ideal gaseous state at 1 atmos pressure were calculated for 12 temperatures, from 100 to 1000°K, using a rigid rotator, harmonic oscillator approximation.

Substituted Methanes. XXIII. Infrared Spectral Data, Rotational Constants, Normal Coordinate Treatments, and Thermodynamic Properties for CD3Br and CH3Br

Infrared spectra were obtained between 400 and 4000 K with NaCl and KBr prisms. The a1 fundamentals for CD3Br are 2157, 993, and 578 K; for CH3Br they are 2972, 1305, and 611 K. For CD3Br, a least squares analysis of the observed wave numbers of the sub‐bands of σ6(e) gave for B1,A1,ζ, and σ0 the values 0.255 K, 2.529 K, 0.150, and 712.3 K; for σ5(e) the values were 0.257 K, 2.530 K, —0.339, and 1056.2 K. For σ4(e)=2293 K, the sub‐bands were not resolved, but the sum rule gave ζ4=0.240. The microwave value of B0 was used. The signs of B1—B0 for σ6 and σ5 are the same as those previously obtained for CH3I by use of the high‐dispersion records of Lagemann and Nielsen. For CH3Br, a least squares analysis of the grating data of Bennett and Meyer gave for σ6(e) : 0.315 K, 5.144 K, 0.217, and 955.4 K; for σ5(e) : 0.304 K, 5.062 K, —0.242, and 1448.2 K; and for σ4(e) : 0.321 K, 5.153 K, 0.064, and 3055.6 K. The sign of B1—B0 for σ6 is the same as for CH3I, but the signs for σ5 and σ4 are reversed. This inconsist...

C13 Isotope Effect in the Thermodecomposition of Ethyl Bromide

The C12—C13 fractionation factor in the decomposition of gaseous ethyl bromide has been measured from 350—450°C, using samples of natural isotope abundance. The rate constants are defined as follows: CH3CH2Br→CH2=CH2+HBrk1,CH3C*H2Br→CH2=C*H2+HBrk2,C*H3CH2Br→C*H2=CH2+HBrk3. At 400°C, the C12 enrichment of the first fraction of ethylene from decomposition of the ethyl bromide is S0≡1+e0=2k1k2+k3=1.0079±0.0006, with a temperature coefficient of — 2.8×10‐5/°C.The primary and secondary isotope effects are defined, respectively, as β=k1/k2—1 and γ=k1/k3—1; thus, to a good approximation, β+γ=2e0. According to theory, β>γ≥0, so that e0 γ≥0. From the data of 400°C one then obtains as an upper limit (k1/k2)max≤1.0159±0.0012. This is significantly lower than the value k1/k2≥1.036 calculated for the rupture of an isolated C—Br bond. The present results, therefore, favor a mechanism involving the direct intramolecular elimination of HBr.

Substituted Methanes. IX. Raman and Infrared Spectra, Assignments, Potential Constants, and Calculated Thermodynamic Properties for CHClBr2 and CDClBr2

Raman displacements, semiquantitative relative intensities, and quantitative depolarization factors for liquid chlorodibromomethane and deuterochlorodibromomethane, and infrared wave numbers and percent transmission curves for both the liquid and gaseous states in the region 400–4300 cm−1 were obtained and compared with previous data. A normal coordinate treatment (Wilson FG matrix method) was carried out, and a consistent set of potential constants for both molecules was determined, using a potential energy function containing all possible 2nd degree terms. Assignments were made for all observed bands. The heat content, free energy, entropy, and heat capacity at constant pressure were calculated for 12 temperatures from 100° to 1000°K.

Isotope Effect on Dissociation Probabilities in the Mass Spectra of Chloroform and Chloroform‐d

The mass spectra of the isotopic molecules CHCl3 and CDCl3 have been determined, using electron energies of 50 v and 70 v. It was found that the probability of dissociation of the C–H bond is approximately three times that for the dissociation of the C—D bond. The relative probability of dissociating H+Cl and D+Cl is the same as the relative probability of obtaining HCl+ and DCl+ ions, namely, about 1.6. Equal probability was observed for the dissociation of H+2Cl and D+2Cl. The probability of removing chlorine atoms is only slightly affected by the deuterium substitution.

C13‐Isotope Effect in the Photolysis of Ethyl Bromide

The photolysis of ethyl bromide in a tenfold excess of cyclopentane has been studied over the temperature range, 30 to 250°C.Ethane is the principal volatile product of reaction. The quantum yield of ethane formation has been found to be unity at 30°C. An increase in apparent quantum yield to 1.5 at 250°C was observed. This increase is attributed to the greater absorption of the incident radiation at high temperatures.The C12 enrichment in the ethane product was 1.0070±0.0008, and invariant in temperature. The isotope fractionation effect is explained on the basis of the higher absorption of C12–C12–Br over C12–C13–Br in the long wavelength region.

Carbon‐13 Isotope Effect in the Thermodecomposition of Nickel Carbonyl

The C12–C13 fractionation factor in the decomposition of gaseous nickel carbonyl has been measured from 30—105°C, using samples of normal isotope abundance. Assuming that the rate‐determining step is the rupture of a Ni–C bond, the rate constants are defined as follows: Ni(CO)4→ lim Ni(CO)3·    +CO  k1, Ni(CO)3C*O−|→Ni(CO)3·   +C*Ok2,→Ni(CO)2C*O·+COk3. The C12 enrichment of the first fraction of CO from decomposition gives, over the temperature range studied, k1/(k2+k3)=1.0222−6.7×10−5t(∘C).The intramolecular and intermolecular isotope effects are defined as k3/3k2 and k1/4k2, respectively. The magnitude of the intramolecular effect was assumed to be given by the square root of the usual reduced mass ratio, with a value of 1.0345. Thus the intermolecular effect calculated from the data becomes, k1/4k2=1.0481−6.7×10−5t(∘C).A theoretical estimate of the magnitude of the intermolecular effect was made using the method of Bigeleisen. Isotopic shifts in vibrational frequencies were computed, and the usual assu...