Intermolecular and intramolecular hydrogen bonding

[Jadaav]

Intermolecular hydrogen bonding is stronger than intramolecular hydrogen bonding.

But how to differentiate between an intermolecular and an intramolecular hydrogen bonding ?

How can I know if there is the presence of an intermolecular or an intramolecular hydrogen bonding in a molecule ?

 

[aclark609]

Intermolecular is BETWEEN molecules. Intermolecular hydrogen bonding most often occurs between molecules involving N, O, F, and of course hydrogen because of their high electronegativities. As far as Intramolecular goes, it's the same rule just WITHIN a molecule rather than BETWEEN molecules.

 

[Jadaav]

Ok thanks. It's clear to me now.

Still can a molecule have both intermolecular and intramolecular hydrogen bonding ?

 

[aclark609]

I don't see why not. As long as there is sufficient electronegativity differences within the molecule, a molecule with intramolecular hydrogen bonding could participate in intermolecular hydrogen bonding as well. It all boils down to opposite charges being attracted to one another.

 

[Yanick]

You must also consider the geometry/size of the molecules. For instance if the H-bond donor and acceptor are positioned in such a way that formation of an intramolecular H-bond would force bond geometries far away from their preferred/stable/equilibrium position then you will strongly disfavor intramolecular H-bonding.

As an example in beta-keto acid decarboxylations, the intermediate is stabilized by an intramolecular H-bond because the bonding geometries form a kind of "six-membered ring" which allows all bond angles and lengths to remain relatively stable ultimately stablilizing the entire intermediate and allowing the reaction to proceed without too much heat added to the system (atleast that's what they tell you in O-Chem). This type of thing will not always be possible in smaller molecules or when the functional groups are positioned in other ways, once again where the geometry of the molecule would force bond strain in order to accomplish an H-bond. Large molecules with many functional groups (like Proteins for instance) rely heavily on intramolecular H-bonding in order to maintain certain conformations but at the same time they will intermolecularly H-bond with water, or maybe other proteins or the substrate etc.

 

[Jadaav]

Ok thanks a lot guys.