<P> These differences can be very small , as in the case of the boiling point of straight - chain alkenes , such as pent - 2 - ene , which is 37 ° C in the cis isomer and 36 ° C in the trans isomer . The differences between cis and trans isomers can be larger if polar bonds are present , as in the 1 , 2 - dichloroethenes . The cis isomer in this case has a boiling point of 60.3 ° C , while the trans isomer has a boiling point of 47.5 ° C. In the cis isomer the two polar C - Cl bond dipole moments combine to give an overall molecular dipole , so that there are intermolecular dipole -- dipole forces ( or Keesom forces ) , which add to the London dispersion forces and raise the boiling point . In the trans isomer on the other hand , this does not occur because the two C − Cl bond moments cancel and the molecule has a net zero dipole ( it does however have a non-zero quadrupole ) . </P>
<P> These differences can be very small , as in the case of the boiling point of straight - chain alkenes , such as pent - 2 - ene , which is 37 ° C in the cis isomer and 36 ° C in the trans isomer . The differences between cis and trans isomers can be larger if polar bonds are present , as in the 1 , 2 - dichloroethenes . The cis isomer in this case has a boiling point of 60.3 ° C , while the trans isomer has a boiling point of 47.5 ° C. In the cis isomer the two polar C - Cl bond dipole moments combine to give an overall molecular dipole , so that there are intermolecular dipole -- dipole forces ( or Keesom forces ) , which add to the London dispersion forces and raise the boiling point . In the trans isomer on the other hand , this does not occur because the two C − Cl bond moments cancel and the molecule has a net zero dipole ( it does however have a non-zero quadrupole ) . </P>
why is the boiling point of the cis isomers higher
why is the boiling point of the cis isomers higher
the two polar C - Cl bond dipole moments combine to give an overall molecular dipole , so that there are intermolecular dipole -- dipole forces ( or Keesom forces ) , which add to the London dispersion forces and raise the boiling point
the two polar C - Cl bond dipole moments combine to give an overall molecular dipole , so that there are intermolecular dipole -- dipole forces ( or Keesom forces ) , which add to the London dispersion forces and raise the boiling point