hydrogen bond

Examples of hydrogen bond in the following topics:

• Hydrogen Bonding and Van der Waals Forces

  • Hydrogen bonds and van der Waals interactions are two types of weak bonds that are necessary to the basic building blocks of life.
  • Two weak bonds that occur frequently are hydrogen bonds and van der Waals interactions.
  • When polar covalent bonds containing hydrogen form, the hydrogen in that bond has a slightly positive charge because hydrogen’s one electron is pulled more strongly toward the other element and away from the hydrogen.
  • This interaction is called a hydrogen bond.
  • Hydrogen bonds are also responsible for zipping together the DNA double helix.

• Water’s States: Gas, Liquid, and Solid

  • The orientation of hydrogen bonds as water changes states dictates the properties of water in its gaseous, liquid, and solid forms.
  • The formation of hydrogen bonds is an important quality of liquid water that is crucial to life as we know it.
  • In liquid water, hydrogen bonds are constantly formed and broken as the water molecules slide past each other.
  • On the other hand, when the temperature of water is reduced and water freezes, the water molecules form a crystalline structure maintained by hydrogen bonding (there is not enough energy to break the hydrogen bonds).
  • Hydrogen bonding makes ice less dense than liquid water.

• Functional Groups

  • This carboxyl group ionizes to release hydrogen ions (H+) from the COOH group resulting in the negatively charged COO- group; this contributes to the hydrophilic nature of whatever molecule it is found on.
  • Other functional groups, such as the carbonyl group, have a partially negatively charged oxygen atom that may form hydrogen bonds with water molecules, again making the molecule more hydrophilic.
  • Hydrogen bonds between functional groups (within the same molecule or between different molecules) are important to the function of many macromolecules and help them to fold properly and maintain the appropriate shape needed to function correctly.
  • Hydrogen bonds are also involved in various recognition processes, such as DNA complementary base pairing and the binding of an enzyme to its substrate.
  • Hydrogen bonds connect two strands of DNA together to create the double-helix structure.

• Covalent Bonds and Other Bonds and Interactions

  • Two types of weak bonds that frequently occur are hydrogen bonds and van der Waals interactions.
  • When polar covalent bonds containing hydrogen are formed, the hydrogen atom in that bond has a slightly positive charge (δ+) because the shared electrons are pulled more strongly toward the other element and away from the hydrogen atom.
  • The weak interaction between the δ+ charge of a hydrogen atom from one molecule and the δ- charge of a more electronegative atom is called a hydrogen bond.
  • For example, hydrogen bonds are responsible for zipping together the DNA double helix.
  • Like hydrogen bonds, van der Waals interactions are weak interactions between molecules.

• Water’s Polarity

  • The two hydrogen atoms and one oxygen atom within water molecules (H2O) form polar covalent bonds.
  • Water's charges are generated because oxygen is more electronegative, or electron loving, than hydrogen.
  • Since water is a nonlinear, or bent, molecule, the difference in electronegativities between the oxygen and hydrogen atoms generates the partial negative charge near the oxygen and partial positive charges near both hydrogens.
  • As a result of water's polarity, each water molecule attracts other water molecules because of the opposite charges between them, forming hydrogen bonds.
  • This interactive shows the interaction of the hydrogen bonds among water molecules.

• Lipid Molecules

  • Saturated fatty acids are saturated with hydrogen since single bonds increase the number of hydrogens on each carbon.
  • If hydrogens are present in the same plane, it is referred to as a cis fat; if the hydrogen atoms are on two different planes, it is referred to as a trans fat.
  • During this hydrogenation process, gas is bubbled through oils to solidify them, and the double bonds of the cis-conformation in the hydrocarbon chain may be converted to double bonds in the trans-conformation.
  • Each singly bonded carbon has two hydrogens associated with it, also not shown.
  • In the trans configuration, the hydrogens are on opposite sides.

• Chemical Reactions and Molecules

  • Chemical reactions occur when two or more atoms bond together to form molecules or when bonded atoms are broken apart.
  • The familiar water molecule, H2O, consists of two hydrogen atoms and one oxygen atom, which bond together to form water .
  • An example of a simple chemical reaction is the breaking down of hydrogen peroxide molecules, each of which consists of two hydrogen atoms bonded to two oxygen atoms (H2O2).
  • The reactant hydrogen peroxide is broken down into water (H2O), and oxygen, which consists of two bonded oxygen atoms (O2).
  • When two hydrogens and an oxygen share electrons via covalent bonds, a water molecule is formed.

• Dehydration Synthesis

  • In dehydration synthesis, monomers combine with each other via covalent bonds to form polymers.
  • The monomers combine with each other via covalent bonds to form larger molecules known as polymers.
  • The removal of a hydrogen from one monomer and the removal of a hydroxyl group from the other monomer allows the monomers to share electrons and form a covalent bond.
  • In the dehydration synthesis reaction between two amino acids, with are ionized in aqueous environments like the cell, an oxygen from the first amino acid is combined with two hydrogens from the second amino acid, creating a covalent bond that links the two monomers together to form a dipeptide.
  • In the dehydration synthesis reaction between two molecules of glucose, a hydroxyl group from the first glucose is combined with a hydrogen from the second glucose, creating a covalent bond that links the two monomeric sugars (monosaccharides) together to form the dissacharide maltose.

• Hydrocarbons

  • Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen, such as methane (CH4).
  • Methane, an excellent fuel, is the simplest hydrocarbon molecule, with a central carbon atom bonded to four different hydrogen atoms .
  • The carbon and the four hydrogen atoms form a shape known as a tetrahedron, with four triangular faces; for this reason, methane is described as having tetrahedral geometry.
  • Double and triple bonds change the geometry of the molecule: single bonds allow rotation along the axis of the bond, whereas double bonds lead to a planar configuration and triple bonds to a linear one.
  • Methane has a tetrahedral geometry, with each of the four hydrogen atoms spaced 109.5° apart.

• Peptide Bonding between Amino Acids

  • The peptide bond is an amide bond which links amino acids together to form proteins.
  • Amino acids are chemical compounds consisting of a carbon atom bonded to an amine group, a hydrogen atom, a carboxylic group, and a varying side-chain (R group); it is this side chain that distinguishes each amino acid from another.
  • The bond that holds together the two amino acids is a peptide bond, or a covalent chemical bond between two compounds (in this case, two amino acids).
  • The amide bond can only be broken by amide hydrolysis, where the bonds are cleaved with the addition of a water molecule.
  • Peptide bonds are amide bonds, characterized by the presence of a carbonyl group attached to an amine.