Answer the following questions:

1. Identify the substitution mechanism (S_N1 or S_N2) and write down the mechanism for the formation of 11 from compound 10 using curly arrows. Although compound 10 has two hydroxyl functional groups, only one was protected. Briefly explain this selectivity.

2. The 1H NMR spectral data for compound 9 is as follows:

¹H NMR (500 MHz, CDCl₃): δ_H 6.85 (d, J = 2.0 Hz, 1H), 6.82 (d, J = 8.5 Hz, 1H), 6.74 (dd, J = 8.5, 2.0 Hz, 1H), 6.60 (s, 1H), 5.55 (s, 1H), 4.00-3.94 (m, 4H), 3.89 (s, 3H), 2.06-2.00 (m, 4H), 1.90 (s, 3H), 1.70-1.65 (m, 4H), 1.20 (s, 1H) ppm

Assign the ¹H NMR peaks to the corresponding hydrogen atom(s) shown in the molecule (Diagram 1, hydrogen environments a-n), giving reasons for their multiplicity, coupling constant and chemical shift values.

Figure

3. The exact procedure for the formation of compound 8 is given below. Calculate the theoretical yield (g) of compound 8. Show the calculation steps involved in the calculation.

8-(Prop-1-en-2-yl)-1,4-dioxaspiro[4.5]decan-8-ol (8).

To a solution of isopropenylmagnesium bromide (0.5 M in THF, 1.8 L, 0.90 mol) was added a solution of 1,4 - dioxaspiro[4.5]decan- 8-one (100 g, 0.64 mol) in THF (200 mL) at a rate to maintain the reaction temperature below 5°C. After complete addition, the reaction mixture was stirred for 2 h. After this time, saturated ammonium chloride (200 mL) was added, and the mixture was extracted with ethyl acetate (2 L). The organic phase was washed with brine (300 mL, ×2), dried over MgSO₄, and concentrated in vacuo to afford 8 as a brown solid (126 g, >99%).

Assessment: A take-home assignment on "The total Organic Synthesis Reactions and Mechanisms

Rationale

The questions will help the students practice their knowledge on chemical reactions in Organic Chemistry acquired during the pre-requisite unit, Organic Chemistry. It will provide the foundation to gain a more in-depth understanding of the mechanisms of some of the central reactions that form the basis of living processes, modern research, and contemporary industrial transformations.

Task

This is a take home, written assignment. The questions will be based on reactions covered during Levels 1 and 2 and may have been combined into a multi-step synthesis.

Students have to analyse the reaction procedure and reactants/products, and attempt questions related to the reaction and its mechanism. Student must also consider the stereo-chemical outcomes of each reaction.

The chemical structures and mechanism can be either hand drawn and/or using computer software.