Degrees of unsaturation = (2·9 + 2 − 10)/2 = 5 → consistent with a benzene ring (4) + one additional π or ring (likely C=O, supported by IR 1715 cm⁻¹ for an ester carbonyl).

Fragment analysis:

• δ 7.30, multiplet, 5H → monosubstituted benzene (C₆H₅).
• δ 1.25 t (3H) + δ 4.15 q (2H) with COSY cross-peak → OCH₂CH₃ (an –OEt group, q at 4.15 indicates O-bound CH₂).
• δ 3.65 s, 2H, no COSY partners → an isolated CH₂ attached to two non-protonated groups; chemical shift 3.65 is consistent with a CH₂ between a phenyl and an ester (–CH₂–CO₂–).

Structure: ethyl phenylacetate (PhCH₂CO₂Et) — fits the formula, IR, and all NMR / COSY data.

Strategy:

1. ¹³C + DEPT-135 — Count all carbons; classify each as CH₃, CH₂, CH, or quaternary. Confirms 2 quaternary aromatic C, 1 C=O, 2 CH₃, 1 CH, plus the rest.
2. HSQC (¹H–¹³C, one-bond) — Pair each ¹H signal to the carbon it is bonded to. Resolves any overlapping ¹H signals via the ¹³C dimension. Now you know which methyl is attached to which carbon, and which CH/CH₂ owns each proton.
3. COSY (¹H–¹H) — Walk through ³J-coupled spin systems. The CH–CH₃ stereocenter will show a clear cross-peak between the methine and its methyl. Identify additional CH₂–CH₂ chains.
4. HMBC (²,³J ¹H–¹³C) — The most important step for connecting fragments through the quaternary aromatic carbons and the carbonyl. Look for cross-peaks from aromatic Hs to the two quaternary aromatic Cs (placing substituents around the ring) and from the methine H / methyl Hs to the carbonyl C (showing how the aliphatic fragment hangs off the C=O).
5. NOESY — After the connectivity is set, NOESY cross-peaks (~5 Å) establish the relative stereochemistry at the CH–CH₃ stereocenter (e.g., is the methyl cis or trans to a nearby aromatic H?).

Together these experiments give a complete structure including stereochemistry without needing X-ray diffraction.