work function

Examples of work function in the following topics:

• The Photoelectric Effect

  • In the photoemission process, if an electron within some material absorbs the energy of one photon and acquires more energy than the work function of the material (the electron binding energy), it is ejected.
  • The number of electrons emitted also changes because the probability that each impacting photon results in an emitted electron is a function of the photon energy.
  • The term $\varphi$ is the work function (sometimes denoted W or ϕ), which gives the minimum energy required to remove a delocalized electron from the surface of the metal.
  • The photocathode contains combinations of materials, such as caesium, rubidium, and antimony, specially selected to provide a low work function, so when illuminated by even very low levels of light, the photocathode readily releases electrons.

• Directed ortho-Metalation

  • Among the most useful reactions for the synthesis of complex molecules are those that achieve direct selective functionalization of a hydrocarbon moiety.
  • Since organometallic reagents function as powerful nucleophiles, selective metal hydrogen exchange, Metalation, would represent a powerful first step to that end.
  • Thanks to the seminal work of V.
  • Many derivatives of common functional groups may serve as DMGs.
  • Two examples of this function are drawn below.

• Organic Reactions Overview

  • What starts as an ether with two alkene units is converted to a ketone with just one alkene functionality.
  • Chemists can analyze starting materials and products to determine structures, but to understand exactly why an organic reaction works, they must determine its mechanism.
  • Identify the function of curved arrow notation in the depiction of organic reactions

• An Introduction to Synthesis

  • All of these products may be transformed subsequently to a host of new compounds incorporating a wide variety of functional groups, and thereby open to even further elaboration.
  • The first is a simple functional group conversion problem, that may initially seem difficult.
  • It is often helpful to work such problems backwards, starting from the product.
  • The 3º-alcohol function in the product suggests formation by a Grignard addition to a ketone, and isobutene appears to be a good precursor to each of these reactants, as shown.
  • The useful approach of working out syntheses starting from the target molecule and working backward toward simpler starting materials has been formalized by Prof.

• Functional Groups

  • Functional groups are atoms or small groups of atoms (two to four) that exhibit a characteristic reactivity when treated with certain reagents.
  • A particular functional group will almost always display its characteristic chemical behavior when it is present in a compound.
  • Because of their importance in understanding organic chemistry, functional groups have characteristic names that often carry over in the naming of individual compounds incorporating specific groups.
  • In the following table the atoms of each functional group are colored red and the characteristic IUPAC nomenclature suffix that denotes some (but not all) functional groups is also colored.

• Comparison of Enthalpy to Internal Energy

  • Internal energy is a state function, meaning its value is dependent only on the current state of the system.
  • Internal energy is generally represented as the sum of work and heat done by or to the system.
  • where w represents work and q represents heat.
  • Similarly, +w means work is done on the system, while -w means work is done by the system.
  • So, even if the heat change can be measured, $\Delta U\neq q$ because some work has been performed.

• Functional Groups

  • Functional groups also play an important part in organic compound nomenclature; combining the names of the functional groups with the names of the parent alkanes provides a way to distinguish compounds.
  • Functionalization refers to the addition of functional groups to a compound by chemical synthesis.
  • In materials science, functionalization is employed to achieve desired surface properties; functional groups can also be used to covalently link functional molecules to the surfaces of chemical devices.
  • Alcohols are a common functional group (-OH).
  • Define the term "functional group" as it applies to organic molecules

• Carbon-Carbon Bond Formation

  • The number of generally useful and well tested reactions for effecting carbon-carbon bond formation, ideally in a regio and stereospecific fashion, is relatively small, compared with reactions used to modify functional groups.
  • With the exception of Friedel-Crafts alkylation, these reactions all give products having one or more functional groups at or adjacent to the bonding sites.
  • As a result, subsequent functional group introduction or modification may be carried out in a relatively straightforward manner.
  • A Diels-Alder cycloaddition would be an attractive first step toward the highly substituted cyclohexane ring in fumagillol, inasmuch as the rigidity of the ring permits good control of functional group location and configuration.
  • Many of the essential reactions used here were not known at the time of Corey's work.

• Carbon-Carbon Bond Formation

  • The 2010 Nobel Prize in chemistry was jointly awarded to Heck, Negishi and Suzuki for their work in developing these coupling reaction
  • The Reppe work is outlined in equation # 1 of the first diagram.
  • The best nickel catalyst was Ni(CO)4, a toxic gas, and recent work by K.P.C.
  • If a nitrile function is substituted for the third alkyne component, substituted pyridines are formed.
  • Here, a hexacarbonyldicobalt complex of an alkyne serves as a neighboring group during the acid-catalyzed opening of the cyclic acetal, and then functions as a reactant in the Pauson-Khand reaction.

• Four-Membered Rings

  • Dimerization and elimination are common side reactions, and other functions may compete in the reaction.
  • Example 4 demonstrates that this approach to azetidine formation works well in the absence of competition.
  • Such electron pair delocalization is diminished in the penicillins, leaving the nitrogen with a pyramidal configuration and the carbonyl function more reactive toward nucleophiles.