3. To purify and identify the product, recrystallization is used in order to purify the product, then melting point and TLC techniques are used to identify the product. Theory 4. In nucleophilic substitution reactions, there are two possibilities, either Sn1 or Sn2. In this particular experiment, an Sn2 reaction
In organic and inorganic chemistry, nucleophilic substitution reactions are the most well studied and useful class of reactions. These reactions can occur by a range of mechanisms, the two studied in this lab are the SN1 and SN2 reactions. In a nucleophilic substitution, the nucleophile is a electron rich chemical species which attacks the positive charge of an atom to replace a leaving group. Since nucleophiles donate electrons, they are defined as Lewis bases. The positive or partially positive atom is referred to as an electrophile.
The first step is where the substrate enters the active site on the enzyme. It is held there by hydrophobic interactions between the exposed non-polar groups of the enzyme residues and the side chain of the substrate. The second step is where the hydroxyl group on Serine 195, aided by the histidine-serine hydrogen bonding, preforms its nucleophilic attack on the carbonyl carbon of an aromatic amino acid. While this happens, it also transfers the hydroxyl hydrogen to the histidine nitrogen. The nucleophilic attack pushes the carbonyl electrons onto the carbonyl oxygen, which forms a short-lived intermediate.
This helps to indicate whether or not the reaction follows Markovnikov’s Rule, which states that the electrophile (E+) will add to the carbon involved in a double bond that produces the most stable carbocation. If the rule is followed, the reaction will proceed according to the mechanism in Figure 1. In the silver nitrate test, the alkyl bromide is added to AgNO3. The rate of precipitation with 2° should be faster than the solution with the 1° alkyl halide. In the sodium iodide test, the alkyl halide is added to sodium iodide in acetone.
Bromination is a type of electrophilic aromatic substitution reaction where one hydrogen atom of benzene or benzene derivative is replaced by bromine due to an electrophilic attack on the benzene ring. The purpose of this experiment is to undergo bromination reaction of acetanilide and aniline to form 4-bromoacetanilide and 2,4,6-tribromoaniline respectively. Since -NHCOCH3 of acetanilide and -NH2 of aniline are electron donating groups, they are ortho/para directors due to resonance stabilized structure. Even though the electron donating groups activate the benzene ring, their reactivities are different and result in the formation of different products during bromination. In acetanilide, the lone pair of the nitrogen is delocalized into the
Therefore, they can undergo electrophilic substitution reaction and the attacking species, in this case, will be an electrophile. The +M effect will result in the concentration of electron density at ortho −and para −positions. However, electrophilic substitution reactions with respect to the haloarene reactions are slow in comparison to benzene reactions. This is because the halogen group present in haloarenes are deactivating because of the –I effect. Hence, electrons are withdrawn from the benzene ring.
With the use of radical chemistry, the cis conformation can be changed into a trans configuration where the esters are on opposite sides of one another. Through the isomerization reaction, the dimethyl maleate’s double bond broke and was formed into a single bond by inputting energy, light. It takes approximately 70-80 kcal/mol of energy to break the bond. This structure was then dimethyl fumarate. The cis and trans isomers are diastereomers of one another.
The next step in the formation of SAN is the graft propagation. Figure 5. Graft propagation mechanism This is the final step of the graft process in which the acrylonitrile and styrene form a copolymer with a butadiene radical. Both final compounds are in form of radicals and can be copolymerized to form a random copolymer. As said before graft process is the base of the synthesis of ABS and it is important to follow the steps in order to obtain the desired product.