What is a Hydrogen Bond?
A hydrogen bond is a relatively weak bond that hydrogen atoms make with the electronegative atoms nitrogen, oxygen or fluorine. Hydrogen bonds are weaker than ionic, covalent, and metallic bonds, but still mildly strong in their own right, with an energy typically between 5 to 30 kJ/mole. In contrast, weak covalent bonds have an energy of about 155 kJ/mol. Hydrogen bonding can either be an intermolecular (between molecules) or intramolecular (between different parts of a molecule) bond. This type of bond can occur in both organic molecules, such as DNA, and inorganic molecules, such as water. Hydrogen bonding is partially responsible for the complex secondary and tertiary structure of proteins. The most ubiquitous and simplest example of hydrogen bonding is in water, where every water molecule is bonded to four adjacent water molecules through hydrogen bonding. The oxygen atom in each water molecule has two lone electrons to offer, which are promptly bonded with by hydrogen atoms in ot
Due to the high electronegativity values of certain elements (e.g. oxygen, nitrogen, fluorine etc.), bonds are formed with between these electronegative elements and hydrogen. If the hydrogen is bonded to an electronegative atom, the positive charge from the electronegative atom’s nucleus will be inclined to attract the single electron orbitting the hydrogen atom, leaving it exposed. This hydrogen is said to be given a ‘delta-positive’ charge. A different electronegative atom may have a slightly negative charge from attracting the electrons from a different atom. Therefore a highly directional bond will form between this slightly positive hydrogen atom and slightly negative electronegative atom. Though individually weak, these bonds are collectively strong, and are frequently found in proteins due to the large number of oxygen and nitrogen atoms present in amino acids. The bonds are usually found between the hydrogen atom in an amino group bonded to the oxygen atom in a carboxyl group,
A hydrogen bond is a special type of attractive interaction that exists between certain chemical groups of opposite polarity. Although stronger than van der Waals forces, the typical hydrogen bond is much weaker than both the ionic bond and the covalent bond. Within macromolecules such as proteins and nucleic acids, it can exist between two parts of the same molecule, and figures as an important constraint on such molecules’ overall shape.
