3F problem 3

[EvaLi_3J]

For which of the following molecules will dipole–dipole interactions
be important: (a) CH4; (b) CH3Cl; (c) CH2Cl2; (d) CHCl3;
(e) CCl4?


Can anyone please explain this for me? I don't quite understand the differences between these for types of molecules.

[claribel charway 1I]

Dipole-dipole moments will exist for b,c, and d. CH4 and CCl4 are completely uniform since the atoms around the central atom are the same. Because of this there is not dipole pull because there’s an even amount of electronegativity around carbon. In the case of CH3Cl, CH2Cl2, and CHCl3 there’s differing electronegativities which causes the dipole pull.

[NRobbins_1K]

It's about the charge symmetry of the molecule. If the electronegativity is evenly distributed around the central atom then it will not be polar since there is no net charge, but if certain regions attract electrons more strongly then there will be a partial charge and polarity will occur. The way to calculate this is through dipole interactions.

[Tiffany Vo 3G]

Dipole-dipole interactions exist between polar molecules because one end of the molecule is more negatively charged while the other end is more positively charged. With a, the molecule is nonpolar because the electronegativity difference between the C-H bond isn't large enough to constitute a permanent dipole. Thus, dipole-dipole interactions are less important for CH4.