bimolecular
(adjective)
Involving two molecules.
Examples of bimolecular in the following topics:
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Elimination
- In elimination, a uni- or bimolecular processes, a molecule loses an H and leaving group and a double bond is formed between vicinal carbon.
- Like nucleophilic substitution, it can occur via unimolecular or bimolecular mechanisms.
- In bimolecular elimination (E2), a base deprotonates a carbon vicinal to a leaving group, and the electrons from the C-H bond form a double bond with the adjacent carbon, displacing the leaving group.
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Molecularity
- A mechanism in which two reacting species combine in the transition state of the rate-determining step is called bimolecular.
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Kinetics
- In a simple bimolecular reaction n & m would both be 1, and the reaction would be termed second order, supporting a mechanism in which a molecule of reactant A and one of B are incorporated in the transition state of the rate-determining step.
- A bimolecular reaction in which two molecules of reactant A (and no B) are present in the transition state would be expected to give a kinetic equation in which n=2 and m=0 (also second order).
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Nucleophilic Substitution
- This will be explained further in the detailed sections on unimolecular and bimolecular forms of nucleophilic substitution.
- Bimolecular nucleophilic substitution (SN2) occurs in a one-step process that can be modeled as:
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Grob Fragmentation
- In the bottom epimer the chlorine atom is not oriented properly, and a slower bimolecular E2 elimination is observed.
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Rate Laws for Elementary Steps
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Substitution and Elimination Reactions of Amines
- The energy diagram shown earlier for a single-step bimolecular E2 mechanism is repeated below.
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The Alkyl Moiety
- We call this description the SN2 mechanism, where S stands for Substitution, N stands for Nucleophilic and 2 stands for bimolecular (defined below).
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The Collision Theory
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Alkene Isomerization
- Unlike the previously described unimolecular isomerizations, this compound is formed by a bimolecular reaction between an electronically excited stilbene and a ground state stilbene molecule.