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Alkanes have the general chemical formula C n H 2n+2. The alkanes range in complexity from the simplest case of methane (CH 4), where n = 1 (sometimes called the parent molecule), to arbitrarily large and complex molecules, like pentacontane (C 50 H 102) or 6-ethyl-2-methyl-5-(1-methylethyl) octane, an isomer of tetradecane (C 14 H 30).
Terminal alkynes, like acetylene itself, are mildly acidic, with pK a values of around 25. They are far more acidic than alkenes and alkanes, which have pK a values of around 40 and 50, respectively. The acidic hydrogen on terminal alkynes can be replaced by a variety of groups resulting in halo-, silyl-, and alkoxoalkynes.
Reduction of alkynes is a useful method for the stereoselective synthesis of disubstituted alkenes. If the cis -alkene is desired, hydrogenation in the presence of Lindlar's catalyst (a heterogeneous catalyst that consists of palladium deposited on calcium carbonate and treated with various forms of lead) is commonly used, though hydroboration ...
The following is a list of straight-chain alkanes, the total number of isomers of each (including branched chains), and their common names, sorted by number of carbon atoms. [ 1 ] [ 2 ] Number of C atoms
Addition reactions apply to alkenes and alkynes. It is because they add reagents that they are called unsaturated. In this reaction a variety of reagents add "across" the pi-bond(s). Chlorine, hydrogen chloride, water, and hydrogen are illustrative reagents. Polymerization is a form of addition.
Alkenes also react with halogens (X 2) to form haloalkanes with two neighboring halogen atoms in a halogen addition reaction. Alkynes react similarly, forming the tetrahalo compounds. This is sometimes known as "decolorizing" the halogen, since the reagent X 2 is colored and the product is usually colorless and odorless. [citation needed]
As with organic compounds, the cis isomer is generally the more reactive of the two, being the only isomer that can reduce alkenes and alkynes to alkanes, but for a different reason: the trans isomer cannot line its hydrogens up suitably to reduce the alkene, but the cis isomer, being shaped differently, can.
Skeletal structures and bond angles of arbitrary alkanes, alkenes, and alkynes. Valence shell electron pair repulsion (VSEPR) theory predicts molecule geometry. [ 11 ] [ 12 ] VSEPR predicts molecular geometry to take the configuration that allows electron pairs to be most spaced out.