Question

We leam chemical reactions and spectroscopic techniques so that we can put them to use in solving problems. Chemists routinely acquire information about molecular structure so that they know with which molecule they are working. For example, a chemist runs a reaction and needs to find out whether the material he or she isolated at the end of the reaction is starting material or product. For the pairs of compounds that follow, propose simple (chemical or spectroscopic) laboratory tests that would tell you which of the two compounds you had. Explain exactly what you would do and exactly what you expect to observe. a cycloalkane vs. an alkene (give a chemical method and a spectroscopic method) b. l-alkene vs. 1-alkyne c. cyclohexanol vs. hexanoic acid

Answer 1

A. Bayer's test: It is test for unsaturation, pink colour of Alkaline Kmno4 disappeared on reacting with Alkene. Cycloalkane won't change the pink colour of kmno4.

Spectroscopic method: IR spectrum gives signal at 3100 cm-1 for sp2 CH stretch and at 1600 for C=C stretch for alkenes . And for cycloalkane gives peak at 2980 for Sp3 CH stretch

B. 1-alkyne gives positive Tollen's test and Fehlings test while 1-alkene not.

Spectroscopic method: IR spectrum of 1-alkyne gives peak at 2150 for carbon -Carbon triple bond and at 1610 for alkene C=C stretch

C. Hexanoic acid gives effervescence with NaHCO3 while cyclohexanol gives H2 gas with Sodium metal.

Spectroscopic method: Hexanoic y gives peaks at 1700 for C=O stretch and at 2600-3400 for OH stretch in the IR spectrum. And cyohenxanol gives peak at 3400 for OH stretch only.