MindMap Gallery Nucleophilic substitution and elimination
Detailed summary of nucleophilic substitution and elimination reactions of halogenated hydrocarbons in organic chemistry, with pictures and text, highlighting the key points! Hope it helps everyone.
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One Hundred Years of Solitude is the masterpiece of Gabriel Garcia Marquez. Reading this book begins with making sense of the characters' relationships, which are centered on the Buendía family and tells the story of the family's prosperity and decline, internal relationships and political struggles, self-mixing and rebirth over the course of a hundred years.
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One Hundred Years of Solitude is the masterpiece of Gabriel Garcia Marquez. Reading this book begins with making sense of the characters' relationships, which are centered on the Buendía family and tells the story of the family's prosperity and decline, internal relationships and political struggles, self-mixing and rebirth over the course of a hundred years.
One Hundred Years of Solitude is the masterpiece of Gabriel Garcia Marquez. Reading this book begins with making sense of the characters' relationships, which are centered on the Buendía family and tells the story of the family's prosperity and decline, internal relationships and political struggles, self-mixing and rebirth over the course of a hundred years.
Project management is the process of applying specialized knowledge, skills, tools, and methods to project activities so that the project can achieve or exceed the set needs and expectations within the constraints of limited resources. This diagram provides a comprehensive overview of the 8 components of the project management process and can be used as a generic template for direct application.
Nucleophilic substitution and elimination
Mainly halogenated hydrocarbons
Can be used as a precursor
Nucleophilic and electrophilic
electrophile
an electron-deficient center
characterized by its ability to react with a negative charge or partial negative charge
Electrophiles are Lewis acids
Lewis acid is not equal to acid
Category: Empty p orbitals (c ions) and induced effects
nucleophile
an electron-rich center
characterized by its ability to react with a positive charge or partial positive charge
nucleophiles are Lewis bases
It is not equal to alkali. Alkalinity is evaluated from a thermodynamic perspective.
A strong nucleophile will give a relatively fast SN2 reaction
strong or weak
Any atom with a localized lone pair can be nucleophilic
π bonds can also function as nucleophiles But the nucleophilicity is not very strong
lone electron pair
induction effect
attacking atom
Difficulty of leaving the group
a good leaving group is the conjugate base of an acid with a pKa<0
SN2
Only primary and secondary halogenated hydrocarbon reactions
Cooperative reaction, no intermediates, one transition state back-side attack
dynamics
Effect of Substrate Structure on Reaction Rate
The greater the steric hindrance, the slower the reaction rate, and the tertiary halogenated hydrocarbons will not react.
The greater the steric hindrance, the higher the activation energy
Nucleophilicity
The stronger the nucleophilicity, the faster the reaction rate
strong or weak
Solvent Effects
Protic solvents
contain a hydrogen atom connected directly to an electronegative atom
Protic solvents have electronegative atoms and lone pairs, which can stabilize sodium ions, and protic solvents also have the ability to form hydrogen bonds with chloride ions, thereby stabilizing positive and negative ions.
polar aprotic solvents
lack such a hydrogen atom
SN2 reactions react faster in polar aprotic solvents
Polar aprotic solvents can only stabilize sodium ions, but due to their position cannot stabilize chloride ions, the system has high energy and is prone to reactions.
Polar aprotic solvents increase the rate of the SN2 process by increasing the energy of the nucleophile, resulting in a smaller Ea
Stereospecificity
Because of back-side attack
Why attack from behind
The negative electron of the leaving group has a high electron density in front, which is not conducive to the attack of nucleophiles.
Molecular orbital (MO) theory
So invert the configuration inversion of configuration
E2
β-H elimination
Synergistic reaction, no intermediates
dynamics
The influence of matrix
Regioselectivity
Zaitsev product
Multiple substituted places produce olefins
Bases with small steric hindrance are easy to form
Hofmann product
Produce olefins at less substituted sites
Bases with large steric hindrance are easy to form, such as:
Different products can be obtained by choosing the appropriate base
Stereoselectivity
Stereoselectivity means obtaining at least two products, one of which is the majority
Stereospecificity
Stereospecificity means that only one configuration of the product is obtained
At this time, there is only one β-H, and there is only one configuration, so one product is obtained
Compared
coplanar: The C-C bond can rotate. The formation of π bond requires parallel overlapping of p orbitals and requires the four groups to be coplanar.
Anti-planar products have less steric hindrance and are easier to form
Whether trans or cis coplanar products are formed depends on the configuration of the halohydrocarbon
There are two β-H, each can be anti-planar, and two products will be obtained
Substituted Cyclohexanes
The steric hindrance is smaller when the substituent is located in the axial direction
Kinetic Isotope Effects in E2
The bond energy of C-D bond is stronger than that of C-H bond, about 1–2 kcal/mol
Breaking of C-D bonds requires more ability, higher activation energy, and slower reaction rate
deuterium isotope effect
kD is smaller than kH
If C−H bond cleavage is a quick step, kH/kD is usually in the range of 3-8
If the C−H bond cleavage is not a quick step, kH/kD is usually in the range of 1-2
SN1
SN1 and E1 appear at the same time
Only tertiary halogenated hydrocarbon reactions
Step-by-step reaction, C ion intermediate
C ion rearrangement, E1 also occurs
negative hydrogen migration
Methyl migration
rate-determining step
Solvents have a significant impact on ionic reactions
Reactions are faster in protic solvents
Protic solvents are more suitable as they stabilize ionic intermediates and transition states, resulting in smaller Ea
Substrate on Ionization Rates
Allyl, benzyl can be SN1 and E1
E1
Only tertiary halogenated hydrocarbon reactions
Step by step reaction to form C ion intermediate
rate-determining step
Regiochemical and Stereochemical Outcomes
Stereochemistry of SN1
both inversion of configuration and retention of configuration
Due to the steric inversion structure of ions, more
Kinetic Isotope Effects in E1
Summarize
Three steps to confirm
Determine the function of the reagent
Analyze the substrate and determine the expected mechanism(s)
Consider any relevant regiochemical and stereochemical requirements
Nucleophilic basic
Nucleophilicity is from a kinetic perspective, depending on how quickly the nucleophile reacts with the substrate.
Alkalinity is from a thermodynamic perspective, judged by the strength of the conjugate acid or the stability of the base.
The strongest induction
Bases with large steric hindrance are mainly eliminated
Substitution and elimination of other substrates
Cyanide NACN
strong Nu moderate base
CN negative ion is not a strong base, and the product is mainly SN2
Tosylates benzenesulfonate
sulfonate ions (RSO3−) is an excellent leaving group
Versatile and versatile
Prepared from the corresponding alcohol
Chiral alcohols will maintain their configuration
Similar to halogenated hydrocarbons, substitution and elimination will occur
alcohol
Hydrooxide (HO−) is a bad leaving group and cannot be directly substituted like halogenated hydrocarbons.
Use a strong acid to convert HO- into a good leaving group H2O, and then substitution occurs
Elimination can also occur under strong acid
Primary and secondary alcohols can also be eliminated
The mechanism is E2 rather than E1 process
synthesis strategy
Primary Substrates
Tertiary Substrates