Question

find the molecular structure of the unknown

Compound 18 is a basic liquid (b.p. 135') which has two functional groups. Only the neutral group reacts with acetic anhydride, UV-transparent; IP-liquid film. 3 signals, diff. types of H Mass Spectrum MASS SPECTRAL DATA Unknown mle - (MM) 89 90 Belative Intensity 7.42 0.37 0.02 Intensity m/e

Answer 1

Solution:

• Basic liquid (amine !) : B.P. 135 C (is shows strong molecular interaction).
• Neutral group reacts with Acetic anhydride : it indicates presence of -OH functional group.
• UV : Transparent : absence of conjugation or unsaturation.
• Mass spectra : - MM : 89 indicates presence of Nitrogen atom (odd mass rule) - M+1 : due 13_C (1.1 % of M )and 15_N (0.38 %), we can deduce no. of cabon atoms using this : - no. of Carbon atoms : (0.37-0.03 (N))/7.42 * 100/1.1 = 4 - M+2 : due to 18_O : 0.2 % of M
• Molecular formula = C₄H₁₁NO : base peak at m/z = 58 (M-31) probably : M- (-CH₂OH)
• IR spectra : broad , strong peak 3100-3500 cm-1 indicates presence of -OH functional group ; 2800-3000 cm-1 ( sp3 C-H stretching) :    1100 cm-1 : C-O stretching.
• 1H-NMR : - 6H (2.2 ppm ; S) : due to two -CH₃ group , probably attached to N. - 2H ((2.3 ppm ; t) : -CH₂-N- group , attached to another -CH₂- . - -2H ((3.5 ppm ; t) : -CH₂-O- group , attached to another -CH₂- .    - 1H (4.5 ppm ; s ) : proton of  -OH group (not coupling due to rapid exchange).

Most probable structure of this compound is : HO-CH₂-CH₂-N-( -CH₃)₂