Question

BOTH 4 and 5

4. For each pair of compounds, predict the one with a higher boiling point. Which compounds have zero dipole moments? a. cis-1,2-dichloroethene or cis-1,2-dibromoethene b. cis- or trans-2,3-dichlorobut-2-ene C. cyclohexene or 1,2-dichlorocyclohexene

Answer 1

aga BBB # BY positive end of Me resultant dipole moment. M>O cis-1,2 dibromoethene (T) ta bond M>O dipole moment direchion cis 1,2- dichloroethene (L) resultant dipole moment (II) has higher boiling point than (I) because it has higher molecular weigh cis -1.2-dichlorobut-2-ene trans-12-dichlorobut-2-ene см3 Сез CM al CH3 dipole moments cancel each other ; M =0 M>o мые сме higher dipole moment are less stable Y and boiling point is lower is therefore, trans- isomer has higher boiling point. It is more stable than the cis- isomer. © Den meso cyclohexene (I) (1) has higher boiling point despite of the fact ' Mo that it has higher dipole momest than (I); 1,2-dichloro-cyclohexene (1) Because of the higher molecular weight of (I), than II).

© (a.) eis 1,2-dimethyl Cyclopentene: strain stable : no ring is there . CH₂ CH3 (6.) trans-1.2-dimethylcyclopentene: CH3 CH₃ unstable ; H3C CH3 It has considerabie ring strain. » unstable; transoid of the ring, adds geometry strain into it. stable; cis-old geometry of the ring double bond ; doessit contain that much strain to be unstable. → unstable Da Double bond at the bridge-head position is very much unstable (Bredt's rute). The p-orbital overlap is very poor. Those orbitals are not paralled to each other for effective overlap. Again the double is also of transoid geometry.
Hope that will resolve the problem :-)