MOLECULAR G VALUES, MAGNETIC SUSCEPTIBILITY ANISOTROPIES, SECOND MOMENT OF CHARGE DISTRIBUTION, AND MOLECULAR QUADRUPOLE MOMENTS IN ETHYLENIMINE AND PYRROLE

The high-field first- and second-order Zeeman effect has been observed in ethylenimine and pyrrole. Only the relative signs of the molecular g values are obtained experimentally. However, the absolute signs are conclusively assigned in both molecules by an analysis of the second moment of the charge distributions or molecular quadrupole moments. For ethylenimine the b axis bisects the CNC angle and lies at an angle of 4° 45′ from the CNC plane (see Figure 1). The a axis also lies nearly in the CNC plane and the c axis is approximately perpendicular to the CNC plane. The measured g values and magnetic suscepttbility anisotropies are gaa = –(0.0422 ± 0.008), gbb = 0.0229 ± 0.0009, gcc = 0.0539 ± 0.0010, 2χaa - χbb - χcc = (16.5 ± 0.7) × 10−6 erg/(G2 mol), and 2Xbb - Xcc - Xaa = (4.6 ± 0.8) × 10−6 erg/(G2 mol). The molecular quadrupole moments are Qaa = (1.3 – 0.6), Qbb = –(2.6 – 0.6), and Qcc = (1.3 – 1.0) all in units of 10−26 esu cm2. Using the known molecular structure allows a determination of the diagonal elements in the paramagnetic susceptibility tensor and the anisotropies in the second moment of the charge distribution. These numbers are χaa = 66.6 ± 1.6, χbb = 77.0 ± 1.6, and χcc = 90.5 ± 1.6 all in units of 10−6 erg/(G2 mol) and 〈a2〉 – 〈b2〉 = 2.2 ± 0.6, 〈b2〉 – 〈c2〉 = 6.4 ± 0.6, and 〈c2) – 〈a2〉 = –(8.6 ± 0.6) all in units of 10−16 cm2. All of the above results in ethylenimine are remarkably similar to recent results obtained for ethylene oxide. For pyrrole the a axis bisects the CNC angle and lies in the molecular plane. The b axis also lies in the molecular plane. The measured g values and magnetic suscepttbility anisotropies are gaa = –(0.0895 ± 0.0010), gbb = –(0.0643 ± 0.0010), gcc = (0.0752 ± 0.0010), 2χaa - χbb - χcc = (50.2 ± 1.0) × 10−6 erg/(G2 mol), and 2χbb -χcc - χaa = (34.6 ± 1.8) × 10−6 erg/(G2 mol). The molecular quadrupole moments are Qaa = 6.6 ± 1.2, Qbb = 5.8 ± 1.6, and Qcc = –(12.4 ± 2.3) in units of 10−26 esu cm2. Using the known molecular structure allows a determination of the diagonal elements in the paramagnetic suscepttbility tensor and the anisotropies in the second moment of the charge distribution. These numbers are χaa = 163.8 ± 1.0, χbb = 160.6 ± 1.0, and χcc = 253.0 ± 1.0 in units of 10−6erg/(G2mol)and 〈a2〉 – 〈b2〉 = 0.5 ± 0.4, 〈b2〉 ± 〈c2〉 = 31.2 ± 0.6, and 〈c2〉 – 〈a2〉 = –(31.7 ± 0.6) in units of 10−16 cm2. Combining the above data with the known bulk magnetic suscepttbility for pyrrole gives the diagonal elements in the total magnetic suscepttbility tensor which are χaa = –(31.9 ± 0.9), χbb = –(37.0 ± 1.1), and χcc = -(76.8 ± 1.5) in units of 10−6 erg/(G2 mol). Also available are the individual elements of the second moment of the charge distribution which are 〈a2〉 = 39.1 ± 0.7, 〈b2〉 = 38.6 ± 0.7, and 〈c2〉 = 7.5 ± 0.7 all in units of 10−16 cm2. The results on pyrrole are compared to the recent values for furan. The magnetic susceptibilities for several ring compounds are discussed in light of local and ring-current anisotropies. © 1969, American Chemical Society. All rights reserved.