SN1 SN2 Comparison

Knowing the reactions is not enough, we have to take a step further: to organize and compare them. There are several aspects that we can compare for the nucleophilic substitution reactions:
  1. Nucleophile
  2. Substrate
  3. Solvent
  4. Leaving Group
  5. Kinetics
  6. Stereochemistry
  7. Rearrangements

1. Nucleophile
SN1: Since a nucleophile is not involved in the rate-determining step, it does not have to be a strong nucelophile (in fact, a strong nucleophile will prefer a SN2 over SN1).
SN2: A strong nucleophile is required to make the concerted reaction feasible.

2. Substrate
SN1: As a carbocation intermediate determines the rate of reaction, a more substitued substrate is needed.
SN2: A crowded substrate will hindered the electrophilic carbon from the attack of the nucleophile. So a bulky substrate is a bad substrate for SN2.

3. Solvent
SN1: The ionization step is rate-determining, so a highly polar (ionizing) protic solvent stabilizes the ions formed.
SN2: It needs energy to strip off the solvent molecule if the nucelophile is solvated by the solvent. So aprotic solvent is better as no hydrongen bonding will be formed.

4. Leaving Group
Both reactions require a good leaving group. 

5. Kinetics 
SN1: the rate of reaction is determined by the concentration of the substrate ONLY as the ionization takes place in the substrate molecule.
SN2: the rate of reaction is determined by the concentration of both the substrate and the nucleophile because it is a concerted reaction.

6. Stereochemistry
SN1: There are two sides a nucleophile can attack the empty p orbitals of the carbocation intermediate. A racemic mixture may be formed. More often, there are more inversion product than the retention product.
SN2: The product formed is always from a back-side attack reaction. In other words, the nucleophile is at the opposite side of the leaving group.

7. Rearrangement 
SN1: Hydride shift or methyl shift may occur to stabilize the carbocation intermediate before the nucleophile attacks.
SN2: As the reaction occurs in one step, there is no rearrangement can be formed.

Here is a table to summarize the comparison:

Comments

Post a Comment

Popular posts from this blog

What is Pepsin?

Image
In Your Body... Pepsin is a digestive enzyme that performed the best in the acidic condition (pH 2) produced by the gastric juice. It digests and breaks down protein (e.g. meat, seeds, eggs, dairy products, etc.). Keep in mind that pepsin digests proteins (not carbohydrates, not fat) into peptides. These peptides are then either absorbed in the intestine or further break down by enzymes from pancreas. In small intestine (pH around 7), pepsin is no longer effective and no longer digests proteins. Hormones Hormones that regulate digestion and hunger such as gastrin and secretin stimulates the production of pepsinogen, the proenzyme of pepsin. In other words, when pepsinogen is activated, it becomes pepsin.
Read more

Intro to 4 Basic Types of Reaction: SN1 SN2 E1 E2 - Updated 2024!

Image
After introducing electrophile and nucleophile, let's talk about SN1 , SN2 , E1 and E2 . Let's see what they mean first: SN1: First-Order Nucleophilic Substitution SN2: Second-Order Nucleophilic Substitution E1: First-Order Elimination E2: Second-Order Elimination   So basically, these 4 types of reactions are categorized into   Nucleophilic Substitution and Elimination .  Nucleophilic Substitution means one thing is substituted by something else, which is a nucleophile (to make it nucleophilic) Elimination always form a double bond product because as something is eliminated, the remained  electrons form a double bond  The condition for each of these reactions are different (solvent, leaving group, reactant bulkiness, etc) and the ability to classify them is crucial. Here is a table summarized all we need to know about them.   source: www.pinstopin.com Our team at Chemistery uses NordVPN every day and we highly recommend it.
Read more

The structure of Chimeric Antigen Receptor (CAR) III - Transmembrane Domains

Image
Transmembrane Domains Among the four components of a chimeric antigen receptor (CAR), the transmembrane domain is the least studied one. How different transmembrane domains affect and contribute to each other's functions is also not well studied. That being said, we will go through the function of a transmembrane domain of a CAR, the CD3ζ transmembrane domain, and the CD8α transmembrane domain.  Introduction of the transmembrane domain The transmembrane domain is where the transmembrane proteins are located. In a CAR, the transmembrane domain has the function to anchor the CAR to the T cell membrane. How strong the CAR is anchored to the T cell membrane affects the CAR expression level and stability.  Currently, the commonly used transmembrane domain is derived from proteins such as CD3ζ, CD4, CD8α, and CD28. The CD3ζ transmembrane domain Among the transmembrane domains mentioned, the CD3ζ transmembrane may improve CAR-mediated T cell action as the CD3ζ transmembrane mediates CAR d
Read more