hydrogenation

Examples of hydrogenation in the following topics:

• Hydrogen Bonding and Van der Waals Forces

  • 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.
  • The slightly negative oxygen side of the water molecule and the slightly positive hydrogen side of the water molecule are attracted to each other and form a hydrogen bond.

• Chemiosmosis and Oxidative Phosphorylation

  • This protein acts as a tiny generator turned by the force of the hydrogen ions diffusing through it, down their electrochemical gradient.
  • The turning of this molecular machine harnesses the potential energy stored in the hydrogen ion gradient to add a phosphate to ADP, forming ATP.
  • The overall result of these reactions is the production of ATP from the energy of the electrons removed from hydrogen atoms.
  • The extra electrons on the oxygen attract hydrogen ions (protons) from the surrounding medium and water is formed.
  • In oxidative phosphorylation, the hydrogen ion gradient formed by the electron transport chain is used by ATP synthase to form ATP.

• 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.
  • Thus, it is more likely that a shared electron would be found near the oxygen nucleus than the hydrogen nucleus.
  • 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.
  • This interactive shows the interaction of the hydrogen bonds among water molecules.

• pH, Buffers, Acids, and Bases

  • Hydrogen ions are spontaneously generated in pure water by the dissociation (ionization) of a small percentage of water molecules into equal numbers of hydrogen (H+) ions and hydroxide (OH-) ions.
  • The hydroxide ions remain in solution because of their hydrogen bonds with other water molecules; the hydrogen ions, consisting of naked protons, are immediately attracted to un-ionized water molecules and form hydronium ions (H30+).
  • An acid is a substance that increases the concentration of hydrogen ions (H+) in a solution, usually by dissociating one of its hydrogen atoms.
  • When bicarbonate ions combine with free hydrogen ions and become carbonic acid, hydrogen ions are removed, moderating pH changes.
  • The pH scale measures the concentration of hydrogen ions (H+) in a solution.

• Covalent Bonds and Other Bonds and Interactions

  • The electron from the hydrogen splits its time between the incomplete outer shell of the hydrogen atom and the incomplete outer shell of the oxygen atom.
  • 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 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.

• Lipid Molecules

  • Glycerol is an alcohol with three carbons, five hydrogens, and three hydroxyl (OH) groups.
  • 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.
  • Each singly bonded carbon has two hydrogens associated with it, also not shown.
  • In the trans configuration, the hydrogens are on opposite sides.

• 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.

• Chemical Reactions and Molecules

  • 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).
  • In the equation below, the reaction includes two hydrogen peroxide molecules and two water molecules.
  • If carbonic acid were added to this system, some of it would be converted to bicarbonate and hydrogen ions.
  • When two hydrogens and an oxygen share electrons via covalent bonds, a water molecule is formed.

• Water’s Heat of Vaporization

  • As a result of the network of hydrogen bonding present between water molecules, a high input of energy is required to transform one gram of liquid water into water vapor, an energy requirement called the heat of vaporization.
  • As liquid water heats up, hydrogen bonding makes it difficult to separate the water molecules from each other, which is required for it to enter its gaseous phase (steam).
  • As a result, water acts as a heat sink, or heat reservoir, and requires much more heat to boil than does a liquid such as ethanol (grain alcohol), whose hydrogen bonding with other ethanol molecules is weaker than water's hydrogen bonding.
  • Eventually, as water reaches its boiling point of 100° Celsius (212° Fahrenheit), the heat is able to break the hydrogen bonds between the water molecules, and the kinetic energy (motion) between the water molecules allows them to escape from the liquid as a gas.
  • The fact that hydrogen bonds need to be broken for water to evaporate means that a substantial amount of energy is used in the process.