Analyzing 1H NMR Data for Structure Elucidation

The provided $^1H$-NMR data is analyzed to determine the structure of the compound. We examine each signal based on its chemical shift ($\delta$), multiplicity (s=singlet, t=triplet, d=doublet, brs=broad singlet), coupling constant ($J$), and integration (number of protons).

Signal Interpretation

• $\delta$ 3.85 (s, 6H): This signal indicates the presence of two equivalent methyl groups. The singlet multiplicity suggests they are not coupled to any nearby protons. This is characteristic of two methoxy ($-\text{OCH}_3$) groups, likely attached to an aromatic ring symmetrically.
• $\delta$ 6.73 (t, 1H, $J = 2.2$ Hz): A triplet integrating for one proton, coupled with a $J$ value of $2.2$ Hz. This suggests a proton influenced by two equivalent neighboring protons.
• $\delta$ 7.1 (d, 2H, $J = 2.2$ Hz): A doublet integrating for two protons, coupled with the same $J$ value of $2.2$ Hz. This indicates two equivalent protons coupled to a single proton. The triplet and doublet pattern with the same coupling constant often arises from meta-coupling in symmetrically substituted aromatic rings.
• $\delta$ 13.05 (brs, 1H): A highly deshielded broad singlet for one proton. This is strongly indicative of an acidic proton, most commonly a carboxylic acid ($-\text{COOH}$) proton.

Structure Identification

Combining these observations:

• The presence of two $-\text{OCH}_3$ groups (6H singlet) and a $-\text{COOH}$ group (1H broad singlet at 13.05 ppm) points towards a substituted benzoic acid.
• The aromatic signals (1H triplet and 2H doublet) suggest a specific substitution pattern on the benzene ring.

Let's consider the structure of 3,5-Dimethoxybenzoic acid:

• It has two equivalent $-\text{OCH}_3$ groups at positions 3 and 5.
• It has a $-\text{COOH}$ group at position 1.
• The protons at positions 2 and 6 (equivalent) are ortho to the $-\text{COOH}$ group and meta to the $-\text{OCH}_3$ groups.
• The proton at position 4 is para to the $-\text{COOH}$ group and ortho to both $-\text{OCH}_3$ groups.

This structure matches the observed NMR data:

• The two $-\text{OCH}_3$ groups give the singlet at $\delta$ 3.85 (6H).
• The $-\text{COOH}$ proton gives the broad singlet at $\delta$ 13.05 (1H).
• The aromatic protons H-2 and H-6 (2H) appear as a doublet around $\delta$ 7.1, coupled to H-4.
• The aromatic proton H-4 (1H) appears as a triplet around $\delta$ 6.73, coupled to H-2 and H-6.
• The coupling constant $J = 2.2$ Hz is typical for meta-coupling in such systems.

Therefore, the compound is 3,5-Dimethoxybenzoic acid.