CHEM 0330 — Organic Chemistry Laboratory 1

CHEM 0330 Study Guide

Organic Chemistry Laboratory 1

This guide connects experimental techniques with the chemical evidence they produce. Pitt's published Fall 2025 CHEM 0330 schedule includes safety and IR, NMR interpretation, extraction and recrystallization, thin-layer chromatography, alcohol dehydration, and a Grignard synthesis. Scope: Pitt CHEM 0330 syllabus and schedule.

These original study notes explain concepts and calculations rather than replace the assigned experiment instructions. Use the instructor-approved procedure, reagent information, protective equipment, and waste guidance for actual lab work. All numerical examples here are invented practice data.

What each technique tells you

Extraction

Liquid–liquid extraction distributes a compound between immiscible phases. The amount in each phase depends on solubility, phase volumes, and chemical form. Acid–base extraction changes the charge state of an acidic or basic compound, often changing which phase it favors. The organic layer is not always the top layer; identify solvents and relevant densities instead of assuming.

Recrystallization

Recrystallization exploits a compound's temperature-dependent solubility to separate it from impurities. A useful solvent system dissolves much more product hot than cold, while impurities behave differently enough to separate. High recovered mass alone does not prove successful purification. Residual solvent or co-crystallized impurities can raise apparent mass.

Thin-layer chromatography

TLC compares movement on a stationary phase under a chosen solvent system. In normal-phase TLC on polar silica, stronger attraction to the plate often reduces travel, while a more strongly eluting mobile phase often increases travel. Rf depends on conditions, so comparisons are most useful on the same plate or under closely matched conditions. Matching one Rf is supporting evidence, not conclusive identification.

Spectroscopy

IR identifies characteristic bond-vibration patterns; NMR provides information about chemical environments and connectivity. Use the whole pattern rather than one peak. IR can support a change in functional group while NMR can reveal residual starting material or unexpected products. Neither a high yield nor one “correct-looking” signal establishes purity by itself.

Synthesis and characterization

Connect the reaction mechanism to the experimental outcome. In alcohol dehydration, consider elimination and possible product distributions. In a Grignard addition, connect the carbon nucleophile and carbonyl electrophile to the resulting carbon skeleton. Moisture sensitivity is chemically meaningful because proton sources can consume a Grignard reagent. Learn the reasoning and use the assigned procedure for execution.

Important vocabulary

Extraction: Transfer of a substance between phases to separate it from other material.
Partition coefficient: Equilibrium concentration ratio for a specified chemical species between two phases.
Distribution ratio: Ratio accounting for all relevant forms of a solute in each phase; it can depend on pH.
Aqueous phase: Water-rich liquid phase.
Organic phase: Phase rich in an organic solvent.
Immiscible: Describes liquids that form separate phases over the relevant composition range.
Emulsion: Dispersion of droplets of one liquid in another that can hinder phase separation.
Drying agent: Material used to remove residual water from an organic phase.
Recrystallization: Purification through dissolution and controlled crystal formation.
Mother liquor: Solution remaining after crystals form.
Vacuum filtration: Filtration assisted by a pressure difference.
TLC: Thin-layer chromatography, an analytical separation on a coated plate.
Stationary phase: Material that remains fixed during chromatography.
Mobile phase: Solvent or mixture moving through the stationary phase.
Eluent: Mobile-phase solvent used for a chromatographic separation.
Rf: Ratio of a spot's travel distance to the solvent front's travel distance.
Limiting reagent: Reactant amount that sets the maximum product amount.
Theoretical yield: Maximum product predicted by the stoichiometric model.
Isolated yield: Amount of product actually collected after workup and purification.
Percent recovery: Recovered amount relative to starting amount in a recovery or purification operation.
Melting range: Temperature interval over which a sample melts under the measurement conditions.
Chemical shift: NMR position reflecting a nucleus's environment.
Integration: Relative NMR signal area, used to estimate proton counts under appropriate conditions.
Multiplicity: Number and pattern of lines in an NMR signal.
Wavenumber: Reciprocal wavelength, commonly cm^{-1} in IR spectroscopy.
Workup: Operations after a reaction that prepare the mixture for product isolation.
Characterization: Measurements used to assess identity and properties of a substance.

Formula and interpretation sheet

Reaction and recovery calculations

n = m/Mmolar; for a liquid, m = ρV when density and temperature are appropriate.
For aA + bB → cC, candidate product from A = nA(c/a); compare candidates from all limiting-reagent possibilities.
Theoretical product mass = theoretical product moles × product molar mass.
Percent yield = isolated actual product/theoretical product × 100%, on the same basis.
Percent recovery = recovered amount/starting amount × 100%. Recovery and reaction yield use different denominators.
Reagent equivalents = reagent moles/reference reagent moles, with the reference explicitly stated.
Atom economy = molar mass of desired product, weighted by its coefficient, divided by total stoichiometric reactant mass per reaction × 100%. This optional sustainability metric differs from yield and excludes many practical process inputs.

Separation and concentration

Rf = distance from baseline to spot center/distance from baseline to solvent front. Both distances use the same origin and units.
K = Corganic/Caqueous for a stated solute species at equilibrium.
If a neutral solute begins in aqueous volume Vaq and is extracted with fresh organic volume Vorg, fraction remaining in water after one ideal extraction is Vaq/(Vaq + KVorg).
With n identical fresh extraction portions, fraction remaining = [Vaq/(Vaq + KVorg)]^{n}, assuming constant K, unchanged phase volumes, and equilibration each time.
Dilution c_{1}V_{1} = c_{2}V_{2} when the amount of solute is conserved.
A standard-curve concentration may be calculated from c = (response − intercept)/slope when within the validated range.

Spectroscopic rules of thumb

Degree of unsaturation DBE = (2C + 2 + N − H − X)/2 for standard closed-shell organic formulas; X counts halogens.
Wavenumber = 1/λ with λ in centimeters for cm^{-1}.
Approximate IR ranges: alcohol O–H often broad around 3200–3600 cm^{-1}; carbonyl C=O commonly in the broad 1650–1800 cm^{-1} region; nitrile C≡N often near 2210–2260 cm^{-1}. Functional group and environment shift these ranges.
Approximate proton NMR regions: many simple alkyl H around 0.5–2 ppm; many H on carbons adjacent to O around 3–4.5 ppm; alkene H around 4.5–6.5 ppm; aromatic H often 6–8.5 ppm; aldehyde H often 9–10 ppm. These are guides, not rigid boundaries.
First-order splitting often follows n + 1 for n equivalent neighboring protons. Exchangeable O–H signals may not follow the simple expectation.

Worked examples

Example 1 Yield

A hypothetical 1:1 reaction begins with 0.500 g of limiting reagent of molar mass 100.0 g/mol. Product molar mass is 150.0 g/mol. Reagent amount = 0.00500 mol, so theoretical product mass = 0.750 g. If 0.600 g dry product is isolated, yield = 0.600/0.750 × 100 = 80.0%. If the sample were wet, its mass would overstate actual product recovery.

Example 2 TLC

The solvent front travels 5.0 cm and the spot center travels 2.0 cm from the baseline. Rf = 2.0/5.0 = 0.40. If two samples each show a spot at 0.40, they might contain the same compound, but different compounds can share an Rf under one solvent system.

Example 3 Repeated extraction

Assume K = 4.0 and Vaq = 20 mL. One extraction with 20 mL organic solvent leaves 20/(20 + 4×20) = 0.20, or 20%, in water. Two fresh 10 mL portions leave [20/(20 + 4×10)]^{2} = 1/9 ≈ 11.1%. The total organic volume is the same, but separate equilibrations improve recovery in this ideal model.

Example 4 Purification result

A 1.00 g crude sample produces 0.72 g recrystallized solid, for 72% mass recovery. This is not automatically a 72% reaction yield. To calculate reaction yield you need the limiting-reagent basis and theoretical product amount. Purity requires additional evidence.

Notebook and report structure

Before the experiment, record the purpose, reaction or separation logic, reagent quantities, molar masses, planned calculations, relevant hazards, and approved waste destinations. During the experiment, record actual observations and quantities as they occur. Afterward, report product amount, appearance, relevant spectral or physical data, and a reasoned interpretation.

In discussion, connect evidence to claims. For example, a reduced starting-material TLC spot, a new product spot, and compatible spectroscopy together support a transformation more strongly than isolated mass alone. Explain losses with specific mechanisms such as incomplete transfer, remaining solubility, side reaction, or incomplete conversion when evidence supports them.

Practice questions and answers

A spot moves 3.0 cm while the front moves 6.0 cm. Rf? 0.50.
A dry sample weighs 0.85 g against a theoretical 1.00 g. Yield? 85%.
Does a single TLC spot prove purity? No; co-elution and detection limits can hide impurities.
Is the organic layer always above water? No; phase position depends on the liquids' densities.
Why can an apparent yield exceed 100%? Residual solvent, impurities, weighing errors, or a mistaken theoretical calculation may inflate it.
Which requires more evidence: “a carbonyl is present” or “the sample is pure acetophenone”? The identity-and-purity claim requires substantially more evidence.

Review routine

For each technique, answer four questions: What property makes the separation or measurement work? What should the result look like? What could produce a misleading result? What second measurement would strengthen the conclusion? Practice yield, recovery, dilution, and Rf calculations without consulting a worked solution.