Organic Chemistry: Techniques & Spectra

📋 Summary — What This Chapter Covers

• Heating under reflux lets a reaction go as far as possible without losing any reactants, products, or solvent by evaporation.
• Distillation separates compounds by boiling point, letting you collect a specific product (e.g. an aldehyde) as it forms and boils off.
• Boiling point determination is used to check the purity and identity of a liquid — impure samples boil over a range and at a higher-than-expected temperature.
• Solvent extraction (separating funnel) separates an organic product from an aqueous layer based on the fact the two liquids don't mix.
• Drying agents (anhydrous salts) remove leftover traces of water from an organic liquid product.
• Mass spectrometry bombards molecules with electrons to form a molecular ion, which fragments into smaller charged pieces — the m/z values of the peaks reveal the molecular mass and structural clues.
• Isotopes show up as multiple peaks (e.g. in halogenoalkanes) because different isotopes have different masses but the same charge.
• Infrared (IR) spectroscopy identifies functional groups by which frequencies of IR radiation are absorbed by particular bonds, shown as absorption peaks at characteristic wavenumbers.

Heating Under Reflux

Here's the problem reflux solves: lots of organic reactions are slow at room temperature. The obvious fix is to heat the mixture up — heat speeds up reactions. But if you just heat an open flask, your volatile reactants, solvent, and product will simply evaporate and escape before the reaction finishes. You'd be boiling away the very things you need.

Reflux solves this by trapping the vapour and sending it back down. A vertical condenser is attached to the top of the flask. As the mixture boils, vapour rises into the condenser, where cold water flowing through the outer "water jacket" cools it back into a liquid — and that liquid drips straight back down into the flask. Nothing escapes; the reaction mixture just keeps circulating and reacting at a raised, controlled temperature.

Typical setup: reaction mixture + anti-bumping granules in a pear-shaped or round-bottomed flask → heated in a heating mantle or water bath → vertical condenser clamped on top (water enters at the bottom, exits at the top — this "counter-current" flow keeps the condenser fully cooled) → joints lightly greased to seal and ease disassembly.

Distillation

doesn't different compounds have different boiling points, so the one with the lowest boiling point evaporates and gets collected first.

primary alcohol → aldehyde lower

Boiling Point Determination

identity purity

Solvent Extraction & Drying

Using a separating funnel

immiscible