Alcohol oxidation and spectral identification

How can one alcohol give two different products?

• Primary propan-1-ol can give propanal or propanoic acid with acidified dichromate. Product removal changes how far oxidation proceeds.
• Choose distillation 蒸馏 for aldehyde 醛 or reflux 回流 with excess oxidant for acid.

Use the alcohol structure

• Primary alcohols can oxidise to aldehydes and acids; secondary alcohols to ketones 酮. Tertiary alcohols resist these stated conditions.
• For propan-2-ol: CH₃CH(OH)CH₃ + [O] → CH₃COCH₃ + H₂O. Dichromate changes orange to green.

Explain purification rather than naming it

• Distillation removes volatile material; reflux returns condensed vapour to the reaction mixture.
• Solvent extraction separates immiscible layers. A suitable anhydrous 无水的 salt removes residual water before final distillation.

Combine mass and IR evidence

• A molecular-ion m/z gives molecular mass for a singly charged ion; the largest peak need not be the molecular ion.
• Use provided IR data to identify possible C=O, O–H, N–H, C=C, C–H and C–X groups. A peak alone rarely identifies one structure.

Reject a competing structure

• C₃H₆O with C=O and a positive warm Fehling’s test fits propanal. Propanone has the same formula and carbonyl but fails that test.
• An acid gives CO₂ with carbonate and has a very broad O–H absorption as well as C=O. Record independent evidence and its limits.

Write from an Mr of 72

• Calculate the relative molecular mass of C4H8O. Use carbon 12, hydrogen 1 and oxygen 16.
• A carbonyl absorption does not by itself prove an aldehyde.