Organic Chemistry Tutoring

Organic chemistry has a reputation as a memorization course. It is closer to a language. Once you see why electrons move, most reactions stop being separate facts and become variations on a few patterns: a nucleophile attacks, a leaving group leaves, a proton moves. Students who memorize reaction lists often hit a wall in the second semester, when there are too many to hold in their heads. STEM Tutor 360's one-on-one organic chemistry tutoring builds the reasoning first, then applies it to problems in the style of your exams.

Sessions cover both semesters, from structure, nomenclature, stereochemistry, and acid-base reasoning, through substitution and elimination, alkenes, alcohols, and aromatic chemistry, to carbonyl chemistry, synthesis, and spectroscopy. Pre-med and pre-dental students are common, since most medical and dental schools require organic chemistry and the material returns on admission exams. We draw mechanisms on a shared whiteboard, and you do the drawing.

A typical organic chemistry problem, worked

2-Bromobutane is treated with sodium ethoxide in ethanol. What is the major product? Then ask what changes if the reagent is sodium cyanide in DMSO.

Start with the substrate. The carbon holding the bromine is attached to two other carbons, so this is a secondary alkyl halide, and it can go either way. Next, classify the reagent. Ethoxide is a strong base as well as a nucleophile. On a crowded secondary carbon, pulling off a neighboring hydrogen is easier than attacking the carbon itself, so E2 beats $\text{S}_{\text{N}}2$.

E2 needs the leaving group and the hydrogen anti to each other, and either neighbor can supply it. Losing a hydrogen from the $\ce{CH2}$ side gives 2-butene. Losing one from the $\ce{CH3}$ side gives 1-butene. The more substituted alkene is more stable, so 2-butene is the major product (Zaitsev's rule), mostly the trans isomer.

Now switch to cyanide in DMSO. Cyanide is a good nucleophile but a weak base, and DMSO is a polar aprotic solvent that leaves the anion relatively free. Substitution wins. $\text{S}_{\text{N}}2$ gives 2-methylbutanenitrile, with inversion of configuration at the carbon that carried the bromine. The decision order is substrate first, then base or nucleophile, then solvent.

Where students usually get stuck

• Memorizing reactions without drawing the mechanism. That fails as soon as a problem changes one detail.
• Curved arrows that start at an atom instead of at a bond or a lone pair.
• Skipping the acid-base check. Find the strongest acid and base present before predicting anything else.
• Assigning R and S without ranking priorities, or flipping a Fischer projection the wrong way.
• Working synthesis problems forward. Working backward from the target, one step at a time, is usually quicker.
• Reading IR and NMR spectra peak by peak instead of starting with the formula and degrees of unsaturation.