Writing the Lab Report: Exp #8 Nucleophilic Substitution

Purpose - what will you learn? - what conclusions will you reach? - a general discussion of theory/expected results is not a purpose!

Results & Discussion - IMPORTANT!!! Results should be presented in Table format

a sample table is included in the lab manual (pg 78) - Organize your discussion as follows:

a) primary structure of the alkyl halide discuss results for both NaI acetone & AgNO3/ethanol include a Table with results that pertain to this section state your expectations for each case discuss your results for each case

do your results agree with your expections? then discuss your results for the next section

Writing the Lab Report: Exp #8 Nucleophilic Substitution

Results & Discussion

b) secondary structure of the alkyl halide discuss results for both NaI acetone & AgNO3/ethanol include a Table with results that pertain to this section state your expectations for each case discuss your results for each case

do your results agree with your expections?c) nature of leaving group (Br- vs Cl) discussion as aboved) solvent polarity for AgNO3 experiments onlye) discuss in general the effect of temperature on reactivity

7 page report limit for this experimentRemember! we did not do concentration experiments - no need to discuss!

do need to understand!!

Experiment 9: Isolation &Identification of an Unknown

Part A: Separation of a Two-Component Mixture by ExtractionPart B: Purification of the Unknown by RecrystallizationPart C: Identification of the Unknown

Review: Mohrig, Hammond & SchatzCh. 11 pgs 113-132 (Extraction)

Ch. 14 pgs 174-182 (Melting Point)Ch. 15 pgs 183-197 (Recrystalization)Ch. 17 pgs 219-235 (Thin Layer Chromatography)

Ch. 20 pgs 277-310 (Infrared Spectroscopy)etc.

The Experiment• Separate a two-component mixture by extraction components: naphthalene (neutral, N)

unknown carboxylic acid or phenol (acidic, AH)

• Isolate the components

Carboxylic acid(acidic)

R CO2HOH

Naphthalene(neutral)

phenol(acidic)

• Purify the unknown acid by recrystallization

• Identify your unknown melting point thin layer chromatography infrared spectroscopy

Getting Started• Come prepared - do a good job on the prelab (more details later) - refresh your knowledge of the techniques you will need - get help before the lab if you need it

• Provided with 1:1 mixture (by weight) of naphthalene and your unknown

• Record your unknown number

• Be sure you know what you are doing before you begin - you will receive only 1 vial of sample (ca. 2 g) - if your need more, it will cost you 10 points

come prepared plan ahead know what you are doing save everything until you are sure it is safe to throw it away

• You will have 2 lab periods to complete this experiment - if you come prepared, you can complete most of the experiment

on the first day

The Separation• Accurately weigh out approximately 2 g of your sample; record• Add CH2Cl2 to the separatory funnel, followed by your sample

- some solids may remain• Extract with NaOH

- use enough base to extract all of your organic acid- mix layers well (don't shake!)

Q! How do I know how much base to use?- Do the math: 1 g unknown ≤ 1 mmol (more is ok!)- check to be sure extracts are basic- extract with a second portion of base

• Separate layers Q! How do I know which layer is which?

density of water: 1.000 g/mL topdensity of CH2Cl2: 1.335 g/mL bottom

Q! What is in each layer?aqueous contains salt of unknown acid (A-)organic contains naphthalene (N)

A-A-

NN

A-

N

The Isolation• Organic Layer (bottom layer) - dry over Na2SO4 - filter into tared flask - evaporate solvent

Q: What is the residue? crude naphthelene (N)

• Aqueous Layer (top layer) - acidify to pH 1 (check with pH paper) - stir well!! Be sure are not just checking the local [acid] - a solid or an oil will form

Q: What is this product? crude unknown (AH)

The Isolation• Aqueous Layer (cont.) If you get a solid - collect by vacuum filtration; dry

If you get an oil (or just a little solid)- transfer all back to separatory funnel - extract product with CH2Cl2

add CH2Cl2 (rinse container as well)separate layers keep organic (bottom) layerdry over Na2SO4filterconcentrate

Q: Why is this product now in the organic layer? - you have neutralized the salt (A- AH)

This is a good place to stop (continue on if you have at least an hour left)

The Purification• Purify unknown acid by recrystallization - use approximately 0.5 g of unknown (record an exact mass) - add warm ethanol dropwise while heating product in hot water bath

use minimum amount of hot solvent to dissolve unknown use of too much solvent will greatly reduce your recovery

- cool once all product has dissolved to room temperature, then in an ice bath

- collect crystals by vacuum filtration wash with a small amount ice cold ethanol

several drops to 1 mL (consider product solubility!) - dry crystals

• If crystals do not form! - DONʼT THROW ANYTHING AWAY your unknown is in there! 1. heat to concentrate (use a boiling stick), then cool again

or 2. add water to the warm solution until it becomes cloudy, then cool - worst case, can evaporate to dryness & start from scratch

This is a better place to stop (crystals can dry thoroughly over the break!)

Identification of the Unknown• Possible unknowns:

• Distinguish between unknowns using IR spectroscopy, melting point, and TLC

Identification of the Unknown1. Distinguish carboxylic acids from phenols using IR spectroscopy

Carboxylic acids- broad OH stretch (ca. 3000 cm-1) - may be diffuse- C=O stretch (ca. 1710 cm-1)

Phenols- OH stretch (ca. 3400 cm-1)

2. Use melting point to distinguish between remaining possibilities- you will need to look up the mp range of all the unknowns (pre-lab)

3. Gain additional support for identification by TLC- must compare your unknown to at least two other compounds

the compounds you choose must make sense based on your data

Repeat characterization steps as needed to arrive at a final identification

Infrared Spectrum of a Carboxylic Acid

OH stretchC=O stretch

O

OHR

Infrared Spectrum of a PhenolOH

OH stretch

NO C=O

Next Week (November 14-18; November 28-December 2)

Isolation & Identification of an Unknown

• Two lab periods are scheduled for this experiment- You will need both days

• This lab report is required- the report is worth 120 points- you may not drop this score- Be sure you are here!

• You will be asked to isolate an unknown by extraction & to identify it using data you collect in the lab

- a brief outline of the procedure is provided in your lab manual- YOU will need to work out the experimental details- it is important to come to lab prepared for this experiment!

There is no lab the week of November 21st

Preparing the PreLab• Title, Purpose, Reference sections are the same as always

• Chemical Properties/Safety Table - must include data for all the unknowns- additional information as relevant (e.g. solvents, other reagents)

• Research Plan - the extraction section should be outlined in flow sheet format

clearly indicate where each component can be found throughoutthe extraction process (e.g. what layer is it in?)

- Specific experimental details must be provided for sections B & C (Recrystalization & Identification of your Unknown)Outline EXACTLY how you plan to proceed

- If you are not sure, GET HELP before the lab begins

• Experimental - on a separate page:

record any deviations from the research planrecord relevant observations / data

Writing the Lab Report: Exp #9 Unknown Due: December 5-9 in your regularly scheduled lab sections (during the required lab checkout)• Include your unknown # in the title of your report, as well as in the body of the paper

• The unknown report should include a complete disussion of the thought process you went through to develop your proposed structure

• DO NOT include experimental detail in the Results & Discussion

• DO discuss:- the color & physical state of your unknown- your IR, melting point, and TLC data- the efficiency and success of your separation & purification procedures- the purity of all compounds you obtained in this experment- EVERYTHING requested- explain how this data supports the identity of your unknown!

• Clearly explain how you eliminated the other four compounds from consideration. Be specific!

• Follow the instructions carefully!

Final Exam

• When: Friday, December 16th, 2011, 10:15 am - 12:15 pm

• Where: Rooms will be announced in the lab & on the website- check the announcements page!

• Format: problems & essay type questions- evaluate a set of data- discuss theory behind individual techniques- make a prediction of what will happen/what your will get based on theory or your knowledge of the technique- calculations of type did in lab reports/questions- This is a closed book exam; you are expected to do your own work

• Let me know ASAP if you require special accommodation- not later than 1 week prior to the exam

• Check the website for additional announcements