Question

Make models of the following compounds, and predict the products formed when they react with the strong bases shown.(c) (d,l)-1,2-dibromo-1,2-diphenylethane + (CH3CH2)3N:

Accepted Answer

Step 1: Analyze the structure of (d,l)-1,2-dibromo-1,2-diphenylethane. This compound contains two bromine atoms attached to adjacent carbon atoms (C1 and C2) in a 1,2-relationship. Each carbon also has a phenyl group (C6H5) attached, and the compound exists as a pair of enantiomers (d and l forms). Step 2: Recall the mechanism of an E2 elimination reaction. E2 eliminations require a strong base (in this case, triethylamine, (CH3CH2)3N) and a β-hydrogen that is anti-coplanar to the leaving group (bromine). Anti-coplanar geometry is crucial for the reaction to proceed efficiently. Step 3: Identify the β-hydrogens on the molecule. For each bromine atom, look at the adjacent carbon (the β-carbon) and determine if it has hydrogens that are anti-coplanar to the bromine. In this case, the β-hydrogens are located on the same carbons as the phenyl groups. Step 4: Predict the product of the E2 elimination. When the β-hydrogens are removed along with the bromine atoms, a double bond will form between C1 and C2. The resulting product will be a trans-stilbene (E-1,2-diphenylethene), as the anti-coplanar geometry favors the formation of the trans isomer. Step 5: Consider stereochemical constraints. Since the starting material is (d,l)-1,2-dibromo-1,2-diphenylethane, the reaction will proceed through the anti-coplanar pathway for each enantiomer, leading to the same trans-stilbene product. Syn-coplanar elimination is unlikely due to the rarity of this pathway and the free rotation around the single bonds.

Make models of the following compounds, and predict the products formed when they react with the strong bases shown.
(c) (d,l)-1,2-dibromo-1,2-diphenylethane + (CH₃CH₂)₃N:

비슷한 문제에 대한 검증된 영상 답변:

주요 개념

E2 Elimination Mechanism

Anti-Coplanar vs. Syn-Coplanar

Steric Hindrance and Conformational Analysis