In organic chemistry, a reaction mechanism is the step by step sequence of reactants, transition state and intermediates by which overall chemical change occurs to afford products
means A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of an overall chemical reaction. The detailed steps of a reaction are not observable in most cases. The conjectured mechanism is chosen because it is thermodynamically feasible, and has experimental support in isolated intermediates (see next section) or other quantitative and qualitative characteristics of the reaction. It also describes each reactive intermediate, activated complex, and transition state, and which bonds are broken (and in what order), and which bonds are formed (and in what order). A complete mechanism must also explain the reason for the reactants and catalyst used, the stereochemistry observed in reactants and products, all products formed and the amount of each.
A. Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are
1. addition reactions,
2. elimination reactions,
3. substitution reactions,
4. pericyclic reactions,
5. rearrangement reactions,
6. photochemical reactions
7. redox reactions.
B. Factors governing organic reactions are essentially the same as that of any chemical reaction. Factors specific to organic reactions are those that determine the stability of reactants and products such as conjugation, hyperconjugation and aromaticity and the presence and stability of reactive intermediates such as free radicals, carbocations and carbanions. An organic compound may consist of many isomers. Selectivity in terms of regioselectivity, diastereoselectivity and enantioselectivity is therefore an important criterion for many organic reactions. The stereochemistry of pericyclic reactions is governed by the Woodward–Hoffmann rules and that of many elimination reactions by Zaitsev's rule.
Organic reactions are important in the production of pharmaceuticals. It was estimated that 20% of chemical conversions involved alkylations on nitrogen and oxygen atoms, another 20% involved placement and removal of protective groups, 11% involved formation of new carbon-carbon bond and 10% involved functional group interconversions.
Reaction type Subtype Comment
1. Addition reactions
1.a. electrophilic addition
include such reactions as halogenation, hydrohalogenation and hydration.
1.b. nucleophilic addition
2. Elimination reaction
include processes such as dehydration and are found to follow an E1, E2 or E1cB reaction mechanism
3. Substitution reactions
3.a. nucleophilic aliphatic substitution
with SN1, SN2 and SNi reaction mechanisms
3.b. nucleophilic aromatic substitution
3.c. nucleophilic acyl substitution
3.d. electrophilic substitution
3.e. electrophilic aromatic substitution
4. Organic redox reactions
are redox reactions specific to organic compounds and are very common.
5. Rearrangement reactions
5.a. 1,2-rearrangements
5.b. pericyclic reactions
means A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of an overall chemical reaction. The detailed steps of a reaction are not observable in most cases. The conjectured mechanism is chosen because it is thermodynamically feasible, and has experimental support in isolated intermediates (see next section) or other quantitative and qualitative characteristics of the reaction. It also describes each reactive intermediate, activated complex, and transition state, and which bonds are broken (and in what order), and which bonds are formed (and in what order). A complete mechanism must also explain the reason for the reactants and catalyst used, the stereochemistry observed in reactants and products, all products formed and the amount of each.
A. Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are
1. addition reactions,
2. elimination reactions,
3. substitution reactions,
4. pericyclic reactions,
5. rearrangement reactions,
6. photochemical reactions
7. redox reactions.
B. Factors governing organic reactions are essentially the same as that of any chemical reaction. Factors specific to organic reactions are those that determine the stability of reactants and products such as conjugation, hyperconjugation and aromaticity and the presence and stability of reactive intermediates such as free radicals, carbocations and carbanions. An organic compound may consist of many isomers. Selectivity in terms of regioselectivity, diastereoselectivity and enantioselectivity is therefore an important criterion for many organic reactions. The stereochemistry of pericyclic reactions is governed by the Woodward–Hoffmann rules and that of many elimination reactions by Zaitsev's rule.
Organic reactions are important in the production of pharmaceuticals. It was estimated that 20% of chemical conversions involved alkylations on nitrogen and oxygen atoms, another 20% involved placement and removal of protective groups, 11% involved formation of new carbon-carbon bond and 10% involved functional group interconversions.
Reaction type Subtype Comment
1. Addition reactions
1.a. electrophilic addition
include such reactions as halogenation, hydrohalogenation and hydration.
1.b. nucleophilic addition
2. Elimination reaction
include processes such as dehydration and are found to follow an E1, E2 or E1cB reaction mechanism
3. Substitution reactions
3.a. nucleophilic aliphatic substitution
with SN1, SN2 and SNi reaction mechanisms
3.b. nucleophilic aromatic substitution
3.c. nucleophilic acyl substitution
3.d. electrophilic substitution
3.e. electrophilic aromatic substitution
4. Organic redox reactions
are redox reactions specific to organic compounds and are very common.
5. Rearrangement reactions
5.a. 1,2-rearrangements
5.b. pericyclic reactions
- Teacher: Dr. أميرة طاهر علي
