Organic Synthesis Booklet: Weighting & Submission Details

Module Weighting and Submission Details for Practical Booklet in Organic Synthesis Reaction

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Marking Scheme

Module weighting: calculation of % yield, reaction mechanism and reporting of melting point: 5%, Spectral interpretation: 5%

Electronic submission of the proforma provided in the practical booklet for teaching block 1 (+ software-drawn structures) via Canvas. The proforma should be downloaded and edited NOT filled in by hand and scanned. Â Scanned documents cannot be marked through speed grader.

1.Carry out an Organic synthetic reaction including isolation, purification and characterisation of product (s).

2.Analyse and interpret spectroscopic data (from any of IR, H-NMR, C-NMR and mass).

3.Draw reaction mechanisms using appropriate drawing software (eg Accelrys, ChemSketch).

4.Calculation of % yield

Section	Marks	Requirements
melting point	4	Melting point reported. Â An appropriate reference for melting point included
% yield calculation	10	Correct calculation of the limiting reagent and the % yield from own data
Reaction mechanism	6	Chemical structures and reaction mechanisms should be drawn with appropriate software such as Accelrys or ChemSketch.
IR spectral analysis	5	Important peaks correctly listed and assigned to the correct functional group
¹H NMR analysis	10 Â	Chemical shifts, multiplicity, integrals and coupling constants correctly assigned to numbered atoms on given structure
¹³C NMR analysis	10	Chemical shifts correctly assigned to numbered atoms on structure given and carbon atoms correctly identified as C, CH, CH₂Â or CH₃.
MS analysis	5	Peaks indicated in the table in the proforma should be accounted for.
Â Â Â	50 marks	Â

1. The hydrogen atoms in propanone are alpha to the carbonyl group (ie they are on an adjacent carbon atom). Hence they are weakly acidic and can be removed with a base to generate a carbanion. This carbanion, which is stabilised via resonance to give an enolate, can also act as a nucleophile and is capable of attacking other carbonyl compounds via nucleophilic attack on the C=O group:

The initial nucleophilic attack on the carbonyl is followed by several subsequent steps, involving transfers of protons and loss of water. These have been described in the lecture course.

2. In this experiment, the product from the condensation reaction between propanone and benzaldehyde is isolated and purified; the product is then identified and characterised using a range of qualitative and spectroscopic methods.

3. Students may work in pairs (but not larger groups) for this experiment.

Note that compound Z is a skin irritant and that appropriate precautions should again be taken to avoid skin contact.

a. Compound â€œZâ€Â is prepared via the following method (note that ZÂ is a skin irritant; any contact with skin should be avoided and disposable gloves must be worn).

b. Prepare a cold solution of sodium hydroxide (2.50 g) in water (25 mL) and methylated spirits (20 mL) in a Quickfit stoppered conical flask. While swirling the flask, add benzaldehyde (2.60 g / 2.5 mL) and Analar propanone (0.80 g / 1.0 mL). Shake the mixture frequently and vigorously in the securely stoppered flask for about fifteen minutes (cool the flask and release the pressure from time to time if necessary) and then allow to stand for a further fifteen minutes in a bath of cold water.

c. Collect the yellow solid product, Z, on a BÃ¼chner funnel and wash it well with cold water to eliminate the alkali. Drain the product thoroughly on the BÃ¼chner funnel.

d. Recrystallise ZÂ from methylated spirit and dry the sample in the vacuum oven.

Determine its melting point.

a. Prepare a solution of Z in methylated spirits (you cannot carry out qualitative tests on a solid in case a precipitate is expected as part of one of the tests). Test for the presence of unsaturation (with bromine in chloroform and with potassium permanganate solution) and for a carbonyl group (with Bradyâ€™s reagent). If colour changes are difficult to see as both starting solutions are similarly coloured, you might have to run appropriate blanks as well.

b. Prepare a Nujol mull of Zand run its infrared spectrum. (Each spectrum may be copied once to give each of the pair a copy; any spectra that have been repeatedly copied will be discounted, no matter who ran the original).

c. Study the provided ¹H and ¹³C NMR spectra and also the mass spectrum.

d. Use all the above information to suggest a structure for compound Z.

Substance (ALL substances to be included)	Chemical Hazard and Risk (H Phrases)	Measures to control Risk (P Phrases) Â
benzaldehyde Â	H302 + H312 Harmful if swallowed or in contact with skin Sigma-Aldrich - B1334 Page 2 of 8 H315 Causes skin irritation.	P280 Wear protective gloves/ protective clothing. P301 + P312 + P330 IF SWALLOWED: Call a POISON CENTER/doctor if you feel unwell. Rinse mouth.
propanone	H225 Highly flammable liquid and vapour. H319 Causes serious eye irritation. H336 May cause drowsiness or dizziness.	P210 Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking. P280 Wear eye protection/ face protection. P304 + P340 + P312 IF INHALED: Remove person to fresh air and keep comfortable for breathing. Call a POISON CENTER/doctor if you feel unwell. P305 + P351 + P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. P337 + P313 If eye irritation persists: Get medical advice/ attention. P403 + P235 Store in a well-ventilated place. Keep cool.
NaOH pellets Â	H290 May be corrosive to metals. H314 Causes severe skin burns and eye damage.	P280 Wear protective gloves/ protective clothing/ eye protection/ face protection. P303 + P361 + P353 IF ON SKIN (or hair): Take off immediately all contaminated clothing. Rinse skin with water/shower. P304 + P340 + P310 IF INHALED: Remove person to fresh air and keep comfortable for breathing. Immediately call a POISON CENTER or doctor/ physician. P305 + P351 + P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
methylated spirits Â	H225 Highly flammable liquid and vapour. H319 Causes serious eye irritation.	P210 Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking. P280 Wear eye protection/ face protection. P305 + P351 + P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. P337 + P313 If eye irritation persists: Get medical advice/ attention. P403 + P235 Store in a well-ventilated place. Keep cool.
bromine water	H314 Causes severe skin burns and eye damage. H330 Fatal if inhaled. H400 Very toxic to aquatic life.	P260 Do not breathe dust/ fume/ gas/ mist/ vapours/ spray. P273 Avoid release to the environment. P280 Wear protective gloves/ protective clothing/ eye protection/ face protection. P284 Wear respiratory protection. P305 + P351 + P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. P310 Immediately call a POISON CENTER or doctor/ physician.