Can someone clarify hydrogen bonding for me?

[hobbitle]

Okay I seem to be a bit confused about hydrogen bonding.

I understand that hydrogen bonds are a strong sub-form of dipole-dipole intermolecular bonds.

I also understand that they 'come into play' when you have a very electronegative atom (typically N, O or F) bonded with a H atom - this results in a very polar molecule.

I guess what I don't understand is if you have two different molecules, how can you tell if they will form hydrogen bonds (a typical question is "Which of these molecules will form hydrogen bonds with water?").  What are the conditions required for *both* molecules in order to form hydrogen bonds?

Here's some example questions:

1) Will H₃COCH₃ form hydrogen bonds with other molecules of the same?  Why?   How would you draw them?
2) Will H₂NCH₂COOH form hydrogen bonds with other molecules of the same?  Why?   How would you draw them?
2) Will (CH₃)₃COH form hydrogen bonds with water? Explain.
4) Will H₃COCH₃ form hydrogen bonds with water? Explain.

Any help in clarifying this, and how to approach these kinds of problems (would you always draw the molecule or can you tell just by looking at the formula?) would be GREATLY appreciated!  Thankyou!

[rhinwarr]

Check to see if the molecule has a polar functional group on it like -OH or -COOH. The hydrogen bonds would be between the H on the end of -OH with the O part of the water molecule. CH3 groups don't form hydrogen bonds because the C and H have approximately the same electronegativities meaning the H isn't really polarised.

[Phenomenol]

Okay I seem to be a bit confused about hydrogen bonding.

I understand that hydrogen bonds are a strong sub-form of dipole-dipole intermolecular bonds.

I also understand that they 'come into play' when you have a very electronegative atom (typically N, O or F) bonded with a H atom - this results in a very polar molecule.

I guess what I don't understand is if you have two different molecules, how can you tell if they will form hydrogen bonds (a typical question is "Which of these molecules will form hydrogen bonds with water?").  What are the conditions required for *both* molecules in order to form hydrogen bonds?

Here's some example questions:

1) Will H₃COCH₃ form hydrogen bonds with other molecules of the same?  Why?   How would you draw them?
2) Will H₂NCH₂COOH form hydrogen bonds with other molecules of the same?  Why?   How would you draw them?
2) Will (CH₃)₃COH form hydrogen bonds with water? Explain.
4) Will H₃COCH₃ form hydrogen bonds with water? Explain.

Any help in clarifying this, and how to approach these kinds of problems (would you always draw the molecule or can you tell just by looking at the formula?) would be GREATLY appreciated!  Thankyou!

1) No. There are no suitable functional groups (eg. -OH) for H-bonding to occur.
2) Yes. -OH and -NH (more specifically than NH2) both have hydrogen, bonded with a highly electronegative atom, thus these two functional groups can interact and form H-bonds. What can also happen is that the OH on one molecule can H-bond with a double bonded O on another molecule.
3) Yes. -OH on the organic compound and H2O will easily H-bond.
4) Yes. The O on the organic compound will H-bond with H2O.

So in short, the conditions for H-bonding to occur is the presence of O-H, N-H or F-H on at least one molecule, and the presence of O, N or F on another molecule (highly electronegative atoms with a lone pair of electrons).