Organic chemistry assignment help works when it explains why electrons move, not just where. Once you see reactions as nucleophiles attacking electrophiles, most mechanisms follow a handful of patterns.
This guide covers the topics in organic coursework, how to draw mechanisms that score, substitution versus elimination, stereochemistry, retrosynthesis and spectroscopy, with worked examples. It ends with how STEM Donkey can prepare a custom solution for study and reference.
Where Organic Chemistry Marks Are Won
Markers reward curly arrows that start from a lone pair or bond and end at an atom or bond, correct charges on every intermediate, a reason for each choice of conditions and spectra assigned peak by peak.
Most lost marks come from arrows drawn backwards, missing formal charges and products given without stereochemistry.
Organic Chemistry Topics We Cover
| Area | Typical assignment tasks |
|---|---|
| Structure and bonding | Hybridization, resonance, acidity and basicity, pKa trends |
| Stereochemistry | R/S and E/Z assignment, enantiomers, diastereomers, meso compounds |
| Substitution and elimination | SN1, SN2, E1 and E2 mechanisms and predicting products |
| Alkenes and alkynes | Electrophilic addition, Markovnikov's rule, hydroboration |
| Carbonyl chemistry | Nucleophilic addition, Grignard reactions, aldol and Claisen reactions |
| Aromatic chemistry | Electrophilic aromatic substitution, directing effects |
| Synthesis | Retrosynthesis, protecting groups, multi-step routes |
| Spectroscopy | IR, 1H and 13C NMR, mass spectrometry, structure determination |
Drawing Mechanisms That Earn Marks
A curly arrow shows the movement of a pair of electrons. It always starts at the electrons, a lone pair or a bond, and points to where they end up.
- Start each arrow at a lone pair or bond, never at a positive charge or a hydrogen atom.
- Use a full arrowhead for an electron pair and a half arrowhead (fishhook) for a single electron in radical reactions.
- Show formal charges on every atom that carries one, in every intermediate.
- Check that charge is balanced across each step.
- Do not exceed an octet on carbon, nitrogen or oxygen; if an arrow forms a new bond, another must break one.
Before drawing, label the nucleophile (electron rich) and the electrophile (electron poor). The first arrow almost always runs from the first to the second.
Substitution Versus Elimination: SN1, SN2, E1 and E2
Choosing between these four mechanisms is one of the most examined skills in organic chemistry. Look at the substrate, the nucleophile or base, the solvent and the temperature together.
| Factor | SN2 | SN1 | E2 |
|---|---|---|---|
| Substrate | Methyl and primary best; tertiary does not react | Tertiary best (stable carbocation) | Secondary and tertiary common |
| Reagent | Strong nucleophile | Weak nucleophile, often the solvent | Strong base, especially bulky |
| Solvent | Polar aprotic, such as DMSO or acetone | Polar protic, such as water or ethanol | Varies; often the base's conjugate acid |
| Rate law | rate = k[RX][Nu] | rate = k[RX] | rate = k[RX][base] |
| Stereochemistry | Inversion of configuration | Largely racemisation | Anti-periplanar H and leaving group |
E1 accompanies SN1 under the same conditions and is favored by heat. In eliminations, the more substituted alkene (Zaitsev product) usually dominates, but a bulky base such as potassium tert-butoxide favors the less substituted (Hofmann) product.
Stereochemistry
Products without stereochemistry are often marked incomplete. Assign configurations using the Cahn-Ingold-Prelog priority rules.
- Rank the four groups on the stereocentre by atomic number of the first atom; higher atomic number wins.
- If two tie, compare the sets of atoms attached to each, moving outward until they differ.
- Point the lowest-priority group away from you.
- Trace 1 → 2 → 3: clockwise is R, anticlockwise is S.
If the lowest-priority group points towards you on a drawing, trace the direction and reverse the answer. For alkenes, the same priorities give Z when the higher-priority groups are on the same side and E when they are opposite.
Retrosynthesis and Multi-Step Routes
Synthesis questions are easier backwards. Retrosynthesis breaks the target into simpler starting materials, one disconnection at a time.
- Identify the functional groups in the target and the bonds that standard reactions can form.
- Disconnect a bond next to a functional group to give two synthons, then find real reagents for each.
- Check that no step will react with another group in the molecule; add a protecting group if needed.
- Write the forward route with reagents and conditions above each arrow.
Worked example: making a tertiary alcohol. Target: 2-methylbutan-2-ol, (CH3)2C(OH)CH2CH3. Disconnect the C-C bond between the carbinol carbon and the ethyl group. That gives acetone as the electrophile and an ethyl anion equivalent as the nucleophile.
Forward route: add ethylmagnesium bromide to acetone in dry ether, then work up with dilute aqueous acid. The Grignard reagent attacks the carbonyl carbon to give an alkoxide, which is protonated to the alcohol. Dry conditions matter, because water destroys the Grignard reagent.
Solving Spectroscopy Problems
Structure determination combines several techniques. Work through them in order and let each one narrow the options.
- From the molecular formula, find the degree of unsaturation: (2C + 2 + N - H - X) / 2.
- Use IR to identify functional groups.
- Use 13C NMR to count carbon environments.
- Use 1H NMR shifts, integrations and splitting to build fragments.
- Join the fragments and check that every peak is explained.
| Feature | Typical IR position (cm-1) | Typical 1H NMR shift (ppm) |
|---|---|---|
| Alcohol O-H | 3200 to 3550, broad | 1 to 5, variable |
| Carboxylic acid O-H | 2500 to 3300, very broad | 10 to 12 |
| C=O (ketone, ester, acid) | 1680 to 1750, strong | Not applicable |
| Aldehyde C-H | about 2720 and 2820 | 9 to 10 |
| Aromatic C-H | just above 3000 | 6.5 to 8 |
| H on carbon next to C=O | Not applicable | 2.0 to 2.7 |
| H on carbon bonded to O | Not applicable | 3.3 to 4.5 |
Worked example: C4H8O2. Degree of unsaturation = (8 + 2 - 8) / 2 = 1, so one ring or double bond. IR shows a strong band near 1740 cm-1, typical of an ester C=O.
1H NMR: δ 4.1 (quartet, 2H), δ 2.0 (singlet, 3H), δ 1.2 (triplet, 3H). The quartet and triplet are an ethyl group, and the 4.1 ppm shift puts its CH2 on oxygen. The singlet at 2.0 ppm is a CH3 next to C=O. The compound is ethyl ethanoate, CH3COOCH2CH3.
Its isomer methyl propanoate would instead show a 3H singlet near 3.7 ppm (OCH3), which is how you tell them apart.
Splitting follows the n + 1 rule for simple cases: a proton with n equivalent neighboring protons appears as n + 1 lines.
Where Organic Chemistry Marks Are Lost
| Mistake | Fix |
|---|---|
| Arrows from positive charges or hydrogen atoms | Start every arrow at a lone pair or bond |
| Five bonds to carbon | Break a bond whenever you form one on a saturated atom |
| SN2 on a tertiary substrate | Check steric hindrance before choosing the mechanism |
| Missing stereochemistry | Show wedges and dashes, and state R/S or racemic |
| Spectra with unexplained peaks | Assign every signal, including integrations |
| Reagents with no conditions | Give solvent, temperature and work-up for each step |
Organic chemistry is a heavy load of patterns at first, but each one carries over to the next reaction. Steady practice pays off.
How STEM Donkey Helps with Organic Chemistry Assignments
Send the problem set or lab handout, any spectra as images or data files, your course's reagent conventions and the rubric. Say whether mechanisms should be hand-drawn style or drawn in ChemDraw-type software.
You receive a custom solution written from scratch, with full mechanisms, reasons for each choice of reagent and conditions, stereochemistry shown and every spectral peak assigned. It is for study and reference, so you can learn the reasoning. Free revisions within the scope of your original request are included.
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Frequently Asked Questions
Mechanisms, substitution and elimination, addition reactions, carbonyl and aromatic chemistry, stereochemistry, retrosynthesis, spectroscopy and organic lab reports.
Look at the substrate first. Methyl and primary substrates with a strong nucleophile in a polar aprotic solvent favor SN2; tertiary substrates with a weak nucleophile in a polar protic solvent favor SN1.
Because it shows the movement of an electron pair. Electrons live in lone pairs and bonds, so that is where every arrow must begin.
Use (2C + 2 + N - H - X) / 2, where X counts halogens. Oxygen and sulfur do not change the result. Each ring or double bond counts as one; a triple bond counts as two.
Yes. Upload the spectra with the molecular formula or proposed compound. The solution assigns each peak from your data and never invents results.
Yes. Each mechanism shows every arrow, intermediate, formal charge and the final product with stereochemistry where relevant.
Deadlines run from 3 hours to 20 days. Multi-step synthesis problems and lab reports need more time than a short mechanism sheet.