Question

2.0000 8.0370 8.0320 8.0197 8.0147 7.2163 6.9190 6.9140 6,9016 6.8966 2.0364 3.8392 3.1765 -0.0441

I need help identifying the compound and interpreta the ir and the nmr spectrum

Answer 1

4-methoxybenzoic acid (p-Anisic acid)

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From Experimental data,

1. It is carboxylic acid (Soluble in NaOH, NaHCO3).

2. Mostly contain an aromatic ring with substituted functional groups (water insoluble, soluble in H2SO4).

3. Melting point = 183.4 - 188.1 oC (Presence of aromatic ring, and H-bonding; non-aromatic compounds have very low melting points).

From IR,

2500 - 2800 cm-1 broad peaks indicated the presence of carboxylic acid functional groups.

3000 - 3100 cm-1 indicated the C-H functional groups possible from phenyl group, 2900 - 3000 cm-1, indicate a possible - CH3 group.

1683 cm-1, confirms the presence of carboxylic acid directly attached to phenyl ring. Usually C=O stretching of COOH observe at 1700-1725 cm1-, but conjugation decrease the frequency, benzoic acid 1689 cm-1).

1264 cm-1, possible C-O stretching, from an ether functional group.

From NMR,

2H, doublet, 8.02 ppm, 2 phenyl hydrogen, at ortho position to electron withdrawing (less donating) functional group - possible carboxylic acid)

2H, doublet, 6.91 ppm, 2 phenyl hydrogen, at ortho postion to an electron donating functional group - possible methoxy functional group)

The doublet confirms the para-substitution, 1 H on each neighboring C-atoms in the phenyl ring)

3H, singlet, 3.84 ppm, confirms the -O-CH3 functional group, attached to the phenyl ring (typically observed at 3.8 ppm).

The above data confirms that the compound is HOOC-Ph-OCH3, 4-methoxybenzoic acid (p-Anisic acid).

Finally, the theoretical melting point = 184 oC, reconfirms the compound