Question

1. for the following pairs of molecules, draw their structures and at least one hydrogen bond connecting them. if no hydrogen bond is possible between these two molecules, indicate that.

a. water and ch₃nh₂
b. methanol (ch₃oh) and carbon dioxide
c. methanol and ch₃nh₂

Explanation:

Step1: Draw water structure

Water ($H_2O$) has an oxygen - centered structure with two hydrogen atoms bonded to the oxygen. The oxygen has two lone - pairs of electrons. The structure is bent.

Step2: Draw $CH_3NH_2$ structure

$CH_3NH_2$ has a carbon atom bonded to three hydrogen atoms and a nitrogen atom. The nitrogen atom is also bonded to two hydrogen atoms and has a lone - pair of electrons.

Step3: Determine hydrogen bond

A hydrogen bond can form between the lone - pair on the nitrogen in $CH_3NH_2$ and a hydrogen atom in water, or between the lone - pairs on the oxygen in water and a hydrogen atom bonded to nitrogen in $CH_3NH_2$.

Step4: Draw methanol structure

Methanol ($CH_3OH$) has a carbon atom bonded to three hydrogen atoms and an $-OH$ group. The oxygen in the $-OH$ group has two lone - pairs of electrons.

Step5: Draw $CO_2$ structure

$CO_2$ is a linear molecule with a carbon atom double - bonded to two oxygen atoms. Each oxygen atom has two lone - pairs of electrons.

Step6: Check hydrogen bond for methanol and $CO_2$

No hydrogen bond is possible between methanol and $CO_2$ because $CO_2$ does not have a hydrogen atom bonded to a highly electronegative atom (N, O, or F) that can act as a hydrogen - bond donor, and while the oxygen in $CO_2$ can be a hydrogen - bond acceptor, methanol's hydrogen atoms are not highly polarized enough towards the $CO_2$ oxygen in a significant hydrogen - bonding way.

Step7: Check hydrogen bond for methanol and $CH_3NH_2$

A hydrogen bond can form between the hydrogen atom of the $-OH$ group in methanol and the lone - pair on the nitrogen in $CH_3NH_2$, or between the hydrogen atom bonded to nitrogen in $CH_3NH_2$ and the lone - pairs on the oxygen in methanol.

Answer:

a. Structures can be drawn as described above and a hydrogen bond is possible.
b. Structures can be drawn as described above and no hydrogen bond is possible.
c. Structures can be drawn as described above and a hydrogen bond is possible.