Key Difference – Elimination vs Substitution Reaction
Elimination and substitution reactions are two types of chemical reactions mainly found in organic chemistry. Thekey differencebetween elimination and substitution reaction can be best explained by using their mechanism.In elimination reaction, rearrangement of previous bonds occurs after the reaction, whereas substitution reaction replaces a leaving group with anucleophile。These two reactions compete with each other and are influenced by several other factors. Those conditions vary from one reaction to another.
What is an Elimination Reaction?
在有机化学中发现了消除反应，该机制涉及从一个或两个步骤中从有机分子中去除两种取代基。当反应以单步机构发生时，它被称为E2 (bi-molecular reaction) reaction, and when it has a two-step mechanism, it is known asE1 (unimolecular reaction) reaction。通常，大多数消除反应涉及至少一个氢原子的损失以形成double bond。This increases the unsaturation of the molecule.
E1反应
什么是替代反应？
替代反应是一种化学反应，涉及另一个功能组在化合物中替换一个功能组。替代反应也称为“单位位移反应”或“单次替代反应”。这些反应在有机化学中非常重要，并且它们主要根据反应所涉及的试剂分为两组：electrophilic substitution reaction and nucleophilic substitution reaction。These two types of substitution reactions exist asSN1反应和sN2 reaction。
替代反应 - 甲烷氯化
What is the difference between Elimination and Substitution Reaction?
Mechanism:
消除反应:消除反应可分为两个美食gories; E1 reactions and E2 reactions. E1 reactions have two steps in the reaction, and E1 reactions have a single step mechanism.
替代反应：Substitution reactions are divided into two categories based on their reaction mechanism: SN1 reactions andSN2个反应。
Properties:
消除反应:
E1反应：These reactions are non-stereospecific, and they follow the Zaitsev (Saytseff) rule. A carbocation intermediate is formed in the reaction so that these reactions are non-concerted reactions. They are unimolecular reactions since the reaction rate depends only on the concentration. These reactions do not take place with primary alkyl halides (leaving groups).Strong acidsare able to promote the loss of OH as H2O or OR as HOR if tertiary orconjugatedcarbocationcan be formed as the intermediate.
E2 reactions:These reactions are stereospecific; anti-periplanar geometry is preferred, but synperiplanar geometry is also possible. They are concerted and considered as bimolecular reactions since the reaction rate depends on the concentration of the base and the substrate. These reactions are favored by strong bases.
替代反应：
SN1个反应：These reactions are said to be non-stereospecific since the nucleophile can attack the molecule from both sides. A stable carbocation is formed in the reaction and therefore these reactions are non-concereted reactions. The rate of the reaction depends only on the concentration of the substrate, and they are called unimolecular reactions.
SN2个反应：These reactions are stereospecific and concerted. The rate of the reaction depends on the concentration of both nucleophile and the substrate. These reactions greatly occur, when the nucleophile is more reactive (more anionic or basic).
Definitions:
Stereospecific:
In a chemical reaction, the production of a particular stereomeric form of the product, regardless of the configuration of the reactant.
Concerted reactions:
协同反应是一种化学反应，其中所有键在一个步骤中断裂并形成。
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