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The concepts of syn and anti addition are used to characterize the different reactions of organic chemistry by reflecting the stereochemistry of the products in a reaction. The type of addition that occurs depends on multiple different factors of a reaction, and is defined by the final orientation of the substituents on the parent molecule.
The Cram's rule of asymmetric induction named after Donald J. Cram states In certain non-catalytic reactions that diastereomer will predominate, which could be formed by the approach of the entering group from the least hindered side when the rotational conformation of the C-C bond is such that the double bond is flanked by the two least bulky groups attached to the adjacent asymmetric center. [3]
For example, dibromocarbene and cis-2-butene yield cis-2,3-dimethyl-1,1-dibromocyclopropane, whereas the trans isomer exclusively yields the trans cyclopropane. [ 4 ] This addition remains stereospecific even if the starting alkene is not isomerically pure, as the products' stereochemistry will match the reactants'.
In organic chemistry, neighbouring group participation (NGP, also known as anchimeric assistance) has been defined by the International Union of Pure and Applied Chemistry (IUPAC) as the interaction of a reaction centre with a lone pair of electrons in an atom or the electrons present in a sigma or pi bond contained within the parent molecule but not conjugated with the reaction centre.
The prominent mechanism is a concerted pathway, meaning that it is a nonpolar, three-centered transition state with retention of stereochemistry. In addition, an S N 2 mechanism, which proceeds with inversion of stereochemistry, or a radical mechanism, which proceeds with obliteration of stereochemistry, are other possible pathways for ...
In chemistry, dynamic stereochemistry studies the effect of stereochemistry on the reaction rate of a chemical reaction. Stereochemistry is involved in: stereospecific reactions; stereoselective or asymmetric reactions; racemisation processes
2,3-sigmatropic rearrangements can offer high stereoselectivity. At the newly formed double bond there is a strong preference for formation of the E- alkene or trans isomer product. The stereochemistry of the newly formed C-C bond is harder to predict.
The addition of Grignard reagents to alkynes is facilitated by a catalytic amount of copper halide. Transmetalation to copper and carbocupration are followed by transmetalation of the product alkene back to magnesium. The addition is syn unless a coordinating group is nearby in the substrate, in which case the addition becomes anti and yields ...