Regarding "hydrogen" bonding
How come the compounds CH2O and CH3OCH3 do not exhibit hydrogen bonding, as opposed to compounds like CH3CH2OH and CH3NH2?
It's indicated in my solutions manual that the two compounds that don't exhibit hydrogen bonding can be H-bond acceptors, not donors. I'm not quite sure what this means...
Thank you!
Frankly I don't know what it means either, especially since HCOOH (is that what you meant by CH2O?) does have hydrogen bonding. Compounds like CH3CH2OH and CH3NH2 have highly electronegative O or N attached to H atoms which makes the N or O slightly - and H slightly + and that's how they H bond. It works the same way with HCOOH. With ethers, however, such as CH3OCH3, the O atom is there but there is no slightly + H atom anywhere to be found. CH3OCH3 isn't highly polar as are the amine, alcohol, and acid.
in order for the hydrogen bond to form in a molecule, the molecule must have an hydrogen atom attached to either oxygen, nitrogen or fluorine. so, the oxygen in C=O bond is not attached to hydrogen and so can't form hydrogen bond.
Hydrogen bonding is a special type of intermolecular force that occurs between a hydrogen atom bonded to a highly electronegative atom (such as O, N, or F) and another electronegative atom in a nearby molecule.
In the case of CH2O (formaldehyde) and CH3OCH3 (dimethyl ether), they do not exhibit hydrogen bonding because they lack the necessary hydrogen atom bonded to a highly electronegative atom.
If we consider CH2O, it has a central carbon atom bonded to two hydrogen atoms and one oxygen atom. While oxygen is electronegative, the hydrogen atom bonded to it is not available for hydrogen bonding because it is not directly bonded to an oxygen, nitrogen, or fluorine atom.
Similarly, in CH3OCH3, the central carbon atom is bonded to three hydrogen atoms and one oxygen atom on each side. Again, the hydrogen atoms in this molecule are not bonded to an oxygen, nitrogen, or fluorine atom and therefore cannot engage in hydrogen bonding.
On the other hand, compounds like CH3CH2OH (ethanol) and CH3NH2 (methylamine) can exhibit hydrogen bonding because they contain a hydrogen atom bonded to an oxygen or nitrogen atom. These hydrogen atoms can act as hydrogen donors and form hydrogen bonds with other suitable acceptor atoms.
In the case of ethanol, the hydrogen atom bonded to the oxygen can engage in hydrogen bonding with other oxygen, nitrogen, or fluorine atoms in nearby ethanol or other molecules.
In methylamine, the hydrogen atom bonded to the nitrogen can also participate in hydrogen bonding with suitable acceptor atoms.
To summarize, compounds that can exhibit hydrogen bonding must have a hydrogen atom directly bonded to an oxygen, nitrogen, or fluorine atom to act as a hydrogen donor. Compounds lacking this specific arrangement, like CH2O and CH3OCH3, cannot participate in hydrogen bonding and instead can act as hydrogen bond acceptors.
Hydrogen bonding occurs when a hydrogen atom is bonded to a highly electronegative atom (such as oxygen, nitrogen, or fluorine) and is also attracted to another electronegative atom nearby. This creates a strong dipole-dipole interaction, resulting in stronger intermolecular forces and higher boiling points.
In the case of CH2O (formaldehyde) and CH3OCH3 (dimethyl ether), both molecules contain oxygen atoms, which are electronegative and can potentially act as hydrogen bond acceptors. However, these compounds do not exhibit hydrogen bonding.
The reason is that in order to engage in hydrogen bonding, a molecule must have a hydrogen atom that is bonded to an electronegative atom (hydrogen bond donor) and another electronegative atom to which it can form a hydrogen bond with (hydrogen bond acceptor).
In CH2O, the oxygen atom is bonded to the carbon atom and acts as the hydrogen bond acceptor. However, the hydrogen atom is not bonded to an electronegative atom, so it cannot act as a hydrogen bond donor. Similarly, in CH3OCH3, the oxygen atoms can act as the hydrogen bond acceptors, but again, the hydrogen atoms are not directly bonded to an electronegative atom, so they cannot act as donors.
On the other hand, in compounds like CH3CH2OH (ethanol) and CH3NH2 (methylamine), hydrogen bonding is observed. In ethanol, the oxygen atom serves as the hydrogen bond acceptor, and the hydrogen atom bonded to the oxygen can act as the donor. Similarly, in methylamine, the nitrogen atom can accept hydrogen bonds, and the hydrogen atom bonded to nitrogen can act as the donor.
So, in summary, compounds CH2O and CH3OCH3 do not exhibit hydrogen bonding because the hydrogen atoms in these compounds are not directly bonded to electronegative atoms, preventing them from acting as hydrogen bond donors. They can only serve as hydrogen bond acceptors.