Question 52

[jgeng03]

I thought H bonding could only occur with O N and F

[sashavazir7501]

your link is broken. The question is wrong.

If you want to rewrite the question weakest bond with hydrogen- or polar covalent bond fine. But Hydrogen bonding is reserved for F O N.

[mcat_premed3832]

Unfortunately, you are incorrect.

First: we apologize for the dead link.

Now to the science:

It is true that H-bonding to an electronegative atom is usually fluorine, oxygen, or nitrogen. But "usually" is not to be confused with "exclusively" especially when dealing with the MCAT.

To begin with sulfur is well know in medicine to engage in H-bonds essential to life itself as you can follow in the link below:

Hydrogen bonds involving sulfur atoms in proteins

Now let's turn our attention to H2S. The fact that H2O is liquid at room temp yet H2S is gas is evidence for the power of H bonds in water. H2S has, however, weak H bonds.

In the Wikipedia article on H-bonds, you will see the weak H bonding involving H2S with HF:

http://en.wikipedia.org/wiki/Hydrogen_bond#Bonding

There are many, many articles about H2S hydrogen bonding to itself. Here are a few:

http://pubs.acs.org/doi/abs/10.1021/j100070a006

Science Direct: H2S hydrogen bonding

http://www3.interscience.wiley.com/journal/110468509/abstract

[acebshaw2450]

I could find articles that also disproved that light always moves at 3 x 10^8 m/s....bravo for research skills. There are no absolutes in science, there are always exceptions, but hydrogen bonds are for N,F,and O. Poor question, without a doubt

[mohsinalam5969]

H-S bonds exhibit weaker hydrogen bonding than H-O, H-N, or H-F bonds (which is why H2S is a gas at RT but water is not), but that doesn't mean they do not hydrogen bond. It's a matter of degree. Hydrogen bonding involving H-S hydrogen bond donors and S hydrogen bond acceptors also happen to have different optical geometric orientations (I'm not sure exactly what it is, but it's not 180 degrees like with the strong hydrogen bond donors and acceptors). The point is, you need to realize that hydrogen bonding isn't some magical thing that all of a sudden happens with O, N, or F. It involves the same electrostatic properties that give us dipole-dipole effects among others, but it's just a term used to describe particularly strong dipole-dipole interactions that occur when two electronegative atoms are bridged by a hydrogen. I feel like the way it is commonly taught makes it seem like it is a different phenomenon, but it's really the same thing.

You can check my description at this sitehttp://forums.studentdoctor.net/showthread.php?t=608326

Read the answer of "SLEEPY 425". I hope this will help all of you in understanding that sulpher can make a weak hydrogen bonding.