Spectroscopy

Mass Spectrometry (MS)

Interpret molecular ion, isotope patterns, nitrogen rule, and hydrogen deficiency index (HDI).

Isotope Pattern (M, M+1, M+2)

Intensity of M peak Intensity of M+1 peak Intensity of M+2 peak

Nominal Mass & Molecular Formula (optional)

Nominal molecular ion mass (integer m/z) Molecular formula

MS Reasoning

Step-by-step interpretation based on fundamental MS rules.

Infrared (IR) — Functional Group Reasoning

Use IR as a filter: confirm or exclude functional groups before structural guessing.

Strong C=O absorption near ~1700 cm⁻¹? — not sure — Yes No If C=O is present: weak C–H absorption at 2700–2850 cm⁻¹? (aldehydic C–H) — not sure — Yes (weak doublet) No Broad O–H / N–H stretch (≈ 3200–3600 cm⁻¹)? — not sure — Yes No Very broad O–H extending down to ~2500 cm⁻¹? (acidic O–H, carboxylic acid) — not sure — Yes No Sharp absorption near ~2100–2260 cm⁻¹? — not sure — Yes No Aromatic C=C bands (~1600 & 1500 cm⁻¹)? — not sure — Yes No

IR Reasoning

What these IR features allow or exclude.

¹H NMR — Diagnostic Protons

Use highly diagnostic protons to distinguish acids, amides, and carbonyl compounds.

Aromatic region signals at ≈ 6.5–8.5 ppm? (aromatic H) — not sure — Yes No Aldehyde proton at ~9–10 ppm? (–CHO) — not sure — Yes No Very downfield broad O–H at ~10–13 ppm? (carboxylic acid O–H) — not sure — Yes No Broad N–H proton at ~5–9 ppm? (amide N–H) — not sure — Yes No

NMR Reasoning

What these NMR features confirm or exclude.

Combine (MS + IR + NMR)

Bring constraints together to narrow structures — using rules, not memorized peaks.

Auto-fill from MS (optional)

Halogen pattern suggested by M+2 — not sure / none — 1 Cl (M : M+2 ≈ 3 : 1) 1 Br (M : M+2 ≈ 1 : 1) 2 Cl (M : M+2 : M+4 ≈ 9 : 6 : 1) 2 Br (M : M+2 : M+4 ≈ 1 : 2 : 1) Nitrogen rule (from nominal mass) — not entered — even nominal mass → even # of N odd nominal mass → odd # of N HDI

IR quick constraints (optional)

Strong C=O near ~1700 cm⁻¹? — unknown — Yes No If C=O is present: weak C–H at 2700–2850 cm⁻¹? (aldehydic C–H) — unknown — Yes (weak doublet) No Broad O–H (alcohol/acid) 3200–3600 cm⁻¹? — unknown — Yes No C≡N / C≡C band near ~2100–2260 cm⁻¹? — unknown — Yes No

NMR quick constraints (optional)

¹H NMR aromatic region (≈ 6.5–8.5 ppm) present? — unknown — Yes No ¹H NMR aldehyde proton (~9–10 ppm) present? — unknown — Yes No ¹H NMR broad acid O–H (~10–13 ppm) present? — unknown — Yes No