Alkylhalides: Substitution reactions 4 (Sn1)

Alkylhalides: Substitution

Nucleophile substitution reaction (Sn1 reaction)

To kick off this new chapter from the alkylhalides, some experimental background theory concerning Sn1 reactions:

the reaction rate of the reaction depends ONLY on the concentration of the alkyl halide (unlike Sn2 reactions where the nucleophile concentration was important aswell !!!).
the reaction rate of the reaction INCREASES if the alkylhalide is more branched at its reaction center (again unlike Sn2 reactions where more branched reaction centers are LESS active !!!). This means a tertiary alkyl bromide f.e. will have a huge relative reaction rate, methylbromide on the other hand will have no Sn1 reaction.
when an alkyl halide reacts with its enantiomere (cfr. stereochemistry), the reaction product will be a racemic mixture (this is a mixture of two enantiomeres of the same compound) or partial racemic product.

Conclusion: this indicates at the presence of a CARBOCATION intermediate

The Sn1 reaction is a two step reaction. The leaving group has already left the alkylhalide before the nucleophile comes in to play. See the example for more details:

Reaction rate Sn1 reaction

The reaction rate of the Sn1 reaction is dependent on the following basic rules:

the better the leaving group the faster the reaction will take place and be finished.
if the carbocation is very very stable, the reaction rate will be high.
the more polar the solvent is, the higher the reaction rate.

as stated before, the concentration of the attacking nucleophile has effect at all on the Sn1 reaction. Why? It is not implemented in the rate-determing step.

Comments

Erythropoietin: definition, structure, synthesis in vivo

Definition: EPO: = erythropoietin A glycoprotein hormon-like structure, a sialoglycoprotein, which is an important factor in the survival, growth and proliferation of erythroid precursor cells (EPC) and it improves the de novo creation, differentation and growth of red blood cells (RBC). Thus, EPO controls the erythropoiesis = production of RBC. EPC: these are cells that are located in the bone marrow, will eventually form the RBC. RBC: cells responsible for the transport and distribution of oxygen throughout the body. Structure: Built out of 165 aminoacids (AA). They are all connected and form 1 polypeptide chain. Although, within the chain, there are 2 disulfide bonds. Respectively on positions: Cys7-161 and Cys29-33 Cys = cystein and the numbers indicate the positions these AA are located. Cystein structure. Available sulfide group for bonding There are also 4 positions where there is a possibility for glycosylation Namel...

The proteasome [1]: a crucial structure of protein degradation

The proteasome Proteins are constantly being synthesized and at the same time being degraded in each cell of our body. One of the most known mechanisms of proteolysis (= protein degradation) is the degradation done by lysosomes. However, an other important mechanism is degradation by the ubiquitin proteasome system (UPS). First of all, it is needed to understand that a cell maintains its protein concentration by a constant turn-over of proteins: when there is a lot of synthesis of a certain protein, this certain protein will also be degraded by a higher level, and vice versa. A protein that has to be degraded will be marked by a polyubiquitin chain which consists of 4 or more ubiquitinmolecules. This protein will be transported to a 26S proteasome. This structure in the cell is built by a 19S part and a 20S part. The 19S part mainly serves as a recognition and binding structure for the polyubiquitinated protein, and the 20S part will destroy the protein. Once attached to the...

Alkynes: addition of H2 gas and Lindlar catalyst

Alkynes: addition of Hydrogen gas (H2) Performing a catalytic reduction on an alkyn will result in giving an alkane. The alkene intermediate will be formed in the process, but will immediately react into an alkane. The end result is just the formed alkane, without stacking of the alkene intermediate. The Lindlar catalyst In theory this is a "poisoned or defected" catalyst. If you use a normal catalyst you will get the above effect with your alkyne. The Lindlar catalyst contains Palladium combined with Calcium-carbonate and treated with Lead. Palladium is the actual catalyst, the calcium carbonate is the carrier of the substance and the lead is the poisonous compound. Using the Lindlar catalyst instead of another catalyst together with Hydrogen gas, will lead into forming the cis-alkene intermediate instead of the forming of the corresponding alkane.

Pharmacist Blog about what I encounter and find useful/interesting

Search This Blog