Organic Pedagogical Electronic
Network
Properties of Hydrogen Bonding
Created by Max Taggart
Edited by Margaret Hilton
Honors Organic Chemistry
Chem 2321 (Sigman), 2013
Hydrogen Bonding
Examples in Nature
Overview: Currently IUPAC defines a hydrogen bond as
an attractive interaction between a hydrogen atom and
an atom that is more electronegative than hydrogen.
The nature of hydrogen bonding began to be studied in
the early 1900’s and is key to understanding many
biological processes, including the structure and function
of proteins and DNA. It also plays a vital role in many
reactions catalyzed by organic catalysts.
Wiki Page: http://en.wikipedia.org/wiki/Hydrogen_bond
Bond Strengths: Hydrogen Vs Covalent
Hydrogen Bonds
Bond Type
Bond Strength (kcal/mol)
Covalent Bonds
Bond Type
Bond Strength (kcal/mol)
[F-H—F]-
39
H2C=CH2
171
[H2O-H—OH3]+
33
Me—H
105
[OH-H—OH]-
23
Ph—I
65
HOH – Cl-
13.5
Et—I
53
COOH – OCOH
7.4
HO—OH
51
I—I
36
HOH – OH2
4.7-5.0
Although hydrogen bonds are weak compared to
covalent bonds, the strongest hydrogen bond strengths
begin to resemble weak covalent bond strengths.
Steiner, T. Angew. Chem. Int. Ed. 2002, 41, 48.
Catalysis of Diels-Alder Reaction
In Diels-Alder reactions involving
conjugated
dienophiles,
hydrogen bonding can help
activate
the
dienophile.
Hydrogen bonding increases the
partial positive charge on the
dienophile
promoting
ring
formation, as shown below.
http://www.princeton.edu/chemistry/macmillan/group-meetings/JBT%20H%20Bonding.pdf
Kelly, T. R. et al. Tet. Lett. 1990, 31, 3381.
Problems
1. Propose a hydrogen bond-catalyzed mechanism
for the following reaction:
2. Rank the following
heteroatoms in order of
decreasing ability to act as an
electron donor in a hydrogen
bond.
3. Propose a mechanism for the following reaction. Consider hydrogen bonding
interactions between the reagents and the catalyst to explain the stereoselectivity of
the product.
Sigman, M. S.; Jacobsen, E. N. J. Am. Chem. Soc. 1998, 120, 4901.
Akiyama, T. et al. Angew. Chem. Int. 2004, 43, 1566.