As shown below, adrenaline (epinephrine) is synthesized when noradrenaline reacts with S-Adenosylmethionine (SAM). Like all SN2 reactions, this conversion involves a nucleophile, an electrophile, and a leaving group, as discussed in class. Your role here is only to identify the three components of the SN2 reaction in the correct order (nucleophile, electrophile, and leaving group): OH OH SAM (S-Adenosylmethionine) Noradrenaline Adrenaline (after loss of proton) Blue, Green, Red Red, Green, Blue Green, Red, Blue Green, Blue, Red
The Correct Answer and Explanation is:
The correct answer is Blue, Green, Red.
This reaction is a classic example of a bimolecular nucleophilic substitution (SN2) reaction, a fundamental process in both organic chemistry and biochemistry. To identify the components correctly, we need to understand their specific roles in the mechanism.
1. Nucleophile (Blue): The nucleophile is the species that donates an electron pair to form a new chemical bond. In this synthesis, the noradrenaline molecule acts as the nucleophile. Specifically, the nitrogen atom of its primary amino group (–NH2), highlighted in blue, possesses a lone pair of electrons. This electron-rich nitrogen atom initiates the reaction by attacking an electron-deficient center.
2. Electrophile (Green): The electrophile is the species that accepts the electron pair from the nucleophile. S-Adenosylmethionine (SAM) is a biological methylating agent. The methyl group (–Me), highlighted in green, is bonded to a positively charged sulfur atom (a sulfonium ion). This positively charged sulfur strongly withdraws electron density from the adjacent methyl carbon, making it highly electron-deficient and thus an excellent electrophile. This is the site that the nucleophilic nitrogen atom attacks.
3. Leaving Group (Red): The leaving group is the atom or group of atoms that detaches from the electrophilic carbon, taking the pair of bonding electrons with it. In an SN2 reaction, the departure of the leaving group occurs at the same time as the nucleophilic attack. When the nitrogen atom of noradrenaline forms a bond with the methyl group, the bond between that methyl carbon and the sulfur atom of SAM must break. The rest of the SAM molecule, which is S-adenosylhomocysteine (outlined in red), is the leaving group. It is a large, stable, and neutral molecule, which makes it a very good leaving group.
Therefore, the correct order of nucleophile, electrophile, and leaving group corresponds to the colors Blue, Green, and Red.
