摘要
用直接量热法测量了五种二氯丁烷位置异构体的标准蒸发焓值,探讨了二氯取代对氯代烷烃液态蒸发焓的影响规律.
By using a LKB-8721-3 precision vaporization calorimeter, enthalpies of vaporization of 2, 2-dichlorobutane, 2, 3-dichlorobutane, 1, 2-dichlorobutane, 1, 3-dichlorobutane and 1, 4-dichlorobutane have been measured, the results being respectively 36.29±0.06, 38.43±0.07, 40.14±0.07, 42.21+0.05, 46.48±0.18kJ/mol. From the above determined enthalpies of vaporization, it can been seen that:
1. At 25℃, enthalpies of vaporization of dichlorobutanes are linearly related to their normal boiling points in ℃:
△H_v^o(25°C, l)=16.2+0.195T_(b.p.) kJ/mol
This is almost the same as the Wadso's equation of △H_v^o-T_(b.p.) for non-associated or slightly associated organic liquids. Therefore the intermolecular london interaction and dipole-dipole interaction are the main interactions between the liquid dichlorobutane molecules.
2. When the number (N_c) of carbon atoms between the two chlorine atoms in a molecule is leas than four, its determined enthalpy of vaporization decreases with the decrease of N_c and is less than that calculated by 'group method', the difference (△) increasing with the decrease of N_c. N_c=4, △=-0.44; N_c=3, △=2.08; N_c=2, △=4.13, N_c=1, △=6.35kJ/mol.
3. When N_c is less than four, the determined intermolecular dipole-dipole interaction energy of dichlorobutane decreases with the decrease of N_c and is less than that calculated by 'group method' significantly, the difference increasing with the decrease of N_c. N_c=4, △=-1.4; N_c= 3, △=1.0; N_c=2, △=3.7; N_c=1, △=4.5 kJ/mol.
4. According to their molar volumes, the average distances between liquid dichlorobutane molecules are approximately equal to those between liquid monochlo-robutane molecules. Thus the differences between determined and calculated enthalpy of vaporization and dipole-dipole intermolecular interaction energy are mainly caused by the charge distribution difference between dichlorobutane molecule and the corresponding monochlorobutane molecule.
出处
《化学学报》
SCIE
CAS
CSCD
北大核心
1992年第10期943-947,共5页
Acta Chimica Sinica
基金
国家自然科学基金
