HUCHEMISTRY

  Valence Or Valency (chemistry) In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Description :- The combining capacity, or affinity of an atom of a given element is determined by the number of hydrogen atoms that it combines with. In methane, carbon has a valence of 4; in ammonia,nitrogen has a valence of 3; in water, oxygen has a valence of 2; and in hydrogen chloride,chlorine has a valence of 1. Chlorine, as it has a valence of one, can be substituted for hydrogen.Phosphorus has a valence of 5 in phosphorus pentachloride, PCl5 . Valence diagrams of a compound represent the connectivity of the elements, with lines drawn between two elements, sometimes called bonds, representing a saturated valency for each element. The two tables below show some examples of different compounds, their valence diagrams, and the valences for each element of the ...

  Wittig Reaction    The Wittig reaction or Wittig olefination is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide called a Wittig reagent. Wittig reactions are most commonly used to convert aldehydes and ketones to alkenes. Most often, the Wittig reaction is used to introduce a methylene group using methylenetriphenylphosphorane (Ph3P=CH2). Using this reagent, even a sterically hindered ketone such as camphor can be converted to its methylene derivative. Reported by :- The Wittig reaction was first reported by Georg Wittig and his coworker Ulrich Schöllkopf. Reported in :- The Wittig reaction was first reported in 1954. Award :- In part for this contribution, Wittig was awarded the Nobel Prize in Chemistry in 1979 .                           Wittig reaction Named after               ...