hydrogenation

(noun)

The chemical reaction of hydrogen with another substance, especially with an unsaturated organic compound, and usually under the influence of temperature, pressure, and catalysts.

Related Terms

  • electrophile
  • substrate
  • nucleophile

(noun)

The chemical reaction of hydrogen with another substance, especially with an unsaturated organic compound.

Related Terms

  • electrophile
  • substrate
  • nucleophile

Examples of hydrogenation in the following topics:

  • Hydrogen Bonding

    • A hydrogen bond is a strong intermolecular force created by the relative positivity of hydrogen atoms.
    • A hydrogen atom attached to a relatively electronegative atom is a hydrogen bond donor.
    • This hydrogen atom is a hydrogen bond donor.
    • Greater electronegativity of the hydrogen bond acceptor will create a stronger hydrogen bond.
    • Where do hydrogen bonds form?
  • Hydrogenation

    • Hydrogenation reactions, which involve the addition of hydrogen to substrates, have many important applications.
    • Hydrogenation refers to the treatment of substances with molecular hydrogen (H2), adding pairs of hydrogen atoms to compounds (generally unsaturated compounds).
    • Most hydrogenation reactions use gaseous hydrogen as the hydrogen source, but alternative sources have been developed.
    • The reverse of hydrogenation, where hydrogen is removed from the compounds, is known as dehydrogenation.
    • Hydrogen gas is the most common source of hydrogen used and is commercially available.
  • The Hydrogen Economy

    • The hydrogen economy refers to using hydrogen as the next important source of fuel.
    • The hydrogen economy refers to a hypothetical future system of delivering energy through the use of hydrogen (H2).
    • There are two primary uses for hydrogen today.
    • Alternatively, liquid hydrogen or slush hydrogen (a combination of liquid and solid hydrogen) can be used.
    • Hydrogen can be stored as a chemical hydride or in some other hydrogen-containing compound.
  • Properties of Hydrogen

    • Hydrogen is the smallest element, with one proton and one electron.
    • Hydrogen exists in two different spin isomers of hydrogen diatomic molecules that differ by the relative spin of their nuclei.
    • Hydrogen is available in different forms, such as compressed gaseous hydrogen, liquid hydrogen, and slush hydrogen (composed of liquid and solid), as well as solid and metallic forms.
    • Because hydrogen is buoyant in air, hydrogen flames ascend rapidly and cause less damage than hydrocarbon fires.
    • Oxidation of hydrogen removes its electron and yields the H+ ion.
  • Hydrogen Bonding

    • Hydrogen forms polar covalent bonds to more electronegative atoms such as oxygen, and because a hydrogen atom is quite small, the positive end of the bond dipole (the hydrogen) can approach neighboring nucleophilic or basic sites more closely than can other polar bonds.
    • In the following diagram the hydrogen bonds are depicted as magenta dashed lines.
    • The molecule providing a polar hydrogen for a hydrogen bond is called a donor.
    • Also, O–H---O hydrogen bonds are clearly stronger than N–H---N hydrogen bonds, as we see by comparing propanol with the amines.
    • Comparison of Boiling Points of Methane, Ammonia, Water, and Hydrogen Fluoride
  • Substitution of the Hydroxyl Hydrogen

    • As with the alcohols, the phenolic hydroxyl hydrogen is rather easily replaced by other substituents.
  • Hydrogenation

    • Addition of hydrogen to a carbon-carbon double bond is called hydrogenation.
    • The simplest source of two hydrogen atoms is molecular hydrogen (H2), but mixing alkenes with hydrogen does not result in any discernible reaction.
    • Catalytic hydrogenation takes place in at least two stages, as depicted in the diagram.
    • First, the alkene must be absorbed on the surface of the catalyst along with some of the hydrogen.
    • This is often true, but the hydrogenation catalysts may also cause isomerization of the double bond prior to hydrogen addition, in which case stereoselectivity may be uncertain.
  • Isotopes of Hydrogen

    • Hydrogen has three naturally occurring isotopes: protium, deuterium and tritium.
    • Hydrogen is generally found as diatomic hydrogen gas H2, or it combines with other atoms in compounds—monoatomic hydrogen is rare.
    • 2H, or deuterium (D), is the other stable isotope of hydrogen.
    • It is a highly unstable isotope of hydrogen.
    • 5H is another highly unstable heavy isotope of hydrogen.
  • Emission Spectrum of the Hydrogen Atom

    • The emission spectrum of atomic hydrogen is divided into a number of spectral series.
    • Further series for hydrogen as well as other elements were discovered as spectroscopy techniques developed.
    • Typically, one can only observe these series from pure hydrogen samples in a lab.
    • Explain how the lines in the emission spectrum of hydrogen are related to electron energy levels.
    • The series limit where n2 is infinite and n1=1 corresponds to the ionization energy of hydrogen.
  • Binary Hydrides

    • Hydrides are compounds in which one or more hydrogen anions have nucleophilic, reducing, or basic properties.
    • A hydride is the anion of hydrogen (H−), and it can form compounds in which one or more hydrogen centers have nucleophilic, reducing, or basic properties.
    • In such hydrides, hydrogen is bonded to a more electropositive element or group.
    • Instead, many compounds have a hydrogen center with a hydridic character.
    • Such bulk transition metals form interstitial binary hydrides when exposed to hydrogen.
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