Question

chapt

Name 3. Chapter 10 covered the synthesis of alkynes by a double dehydrohalogenation of dihalides. A student tried to convert trans-hex-2-ene to hex-2-yne by adding bromine across the double bord then doing a double elimination. The infrared and mass spectra are shown below. Bra 2 NaNH2 100 Relative Intensity Or 75 m/z a Do the spectra confirm the right product? If not what is it? b. Explain the important peaks in the IR.

Answer 1

Question-3: Product is Alkyne

Confirmed by Mass 82 (molecular ion, M), 67 (M-15), 55 (M-27).

IR wave number at about 2200 (weak -C $\equiv$ C-) disubstituted alkyne, absence of strong -C=C-H stretching at about 3100

Question-4:

The mass spectrum corresponds to product (122 molecualr ion), the peak at 29 is due to the fragmentation ion (C2H5 +)

The variation in IR frequency may be due to the partial isomerization of 1,4-diene to stable 1,3-diene form at higher temperature. or may be due to ring expansion to cycloheptadinene with -CH2-CH3 (ethyl as substitution at C3)