📝 Common Synonyms & Alternative Names

Structural Representation of DMF

    CH₃       O
      \       ‖
       N --- C --- H
      /
    CH₃
      

The C–N bond has significant double-bond character due to resonance (see Section 3)

🔬 Overall Geometry: The heavy-atom backbone of DMF (N–C–O) is essentially planar due to resonance delocalization across the amide system. The two methyl groups lie above and below this plane. The molecule is approximately trigonal planar at both nitrogen and the carbonyl carbon, consistent with sp² hybridization of both centers.

💡 Restricted Rotation - The NMR Consequence

The rotational barrier about the C–N bond in DMF is approximately 15–17 kcal/mol - high enough that the two N-methyl groups are inequivalent at room temperature on the NMR timescale. In ¹H NMR (CDCl₃), they appear as two distinct singlets at approximately δ 2.89 ppm (trans-methyl) and δ 2.97 ppm (cis-methyl), plus the formyl proton at δ 7.95 ppm. These three signals are the definitive NMR fingerprint of DMF.

💡 Key distinction: DMF is the tertiary amide of formic acid. The absence of any N–H bond is what makes DMF aprotic. Compare it to formamide (H₂NCHO) which is protic and has very different solvent behavior despite the same core C–N–C=O framework.

Molecular formula: C₃H₇NO

──────────────────────────

C: 3 × 12.011 = 36.033

H: 7 × 1.008 =  7.056

N: 1 × 14.007 = 14.007

O: 1 × 15.999 = 15.999

──────────────────────────

Total MW = 73.095 ≈ 73.09 g/mol

✅ Concentration Reference: Pure DMF at 25 °C has a molarity of 12.92 M (moles per litre). This value is analogous to the "neat" molarity of common solvents and is used when DMF serves as both solvent and reactant in Vilsmeier-Haack formylations or other reagent-grade applications.

💡 Analytical QC Tip: The most reliable IR marker for identifying DMF is the amide carbonyl stretch at 1678 cm⁻¹. Its position significantly below a typical ketone C=O (~1715 cm⁻¹) or aldehyde C=O (~1725 cm⁻¹) immediately confirms the amide functional group. Absence of any N–H stretch (3100–3500 cm⁻¹) confirms the tertiary amide identity.

Q1 · What is the molecular formula of DMF?

The molecular formula of DMF is C₃H₇NO. It contains 3 carbon atoms, 7 hydrogen atoms, 1 nitrogen atom, and 1 oxygen atom. Its SMILES notation is CN(C)C=O and its CAS number is 68-12-2.

Q2 · What is the molecular weight of dimethylformamide?

The molecular weight (molar mass) of dimethylformamide is 73.09 g/mol. The exact monoisotopic mass is 73.0528 Da. This value is used for stoichiometric calculations, mole-fraction concentration determination, and residual solvent limit calculations in pharmaceutical analysis.

Q3 · Why does DMF show two NMR peaks for the methyl groups?

The two N-methyl groups in DMF are chemically inequivalent because the C–N bond has partial double-bond character (due to amide resonance), which restricts rotation. One methyl is cis to the carbonyl oxygen; the other is trans. At room temperature, this restricted rotation is slow on the NMR timescale, producing two distinct singlets at approximately δ 2.89 ppm and δ 2.97 ppm in CDCl₃.

Q4 · What is the chemical structure of DMF?

DMF has the structural formula (CH₃)₂N–CHO. It consists of a formyl group (–CHO) attached to a dimethylamino nitrogen [–N(CH₃)₂]. The nitrogen and carbonyl carbon are both sp² hybridized and essentially coplanar. Resonance delocalization between the nitrogen lone pair and the carbonyl makes the C–N bond shorter than a typical single bond and gives DMF its high polarity.

Q5 · Is DMF an amide or an amine?

DMF is an amide - specifically a tertiary amide (no N–H bond), because it has a carbonyl group (C=O) directly bonded to the nitrogen. It is the N,N-dimethyl derivative of formic acid's amide. While its nitrogen might appear amine-like, the presence of the adjacent C=O completely changes the chemistry: the nitrogen lone pair is delocalized into the carbonyl, making DMF only very weakly basic - far less basic than a simple amine like dimethylamine.

Q6 · What is the SMILES and InChI Key for DMF?

The canonical SMILES for DMF is CN(C)C=O.
The InChI string is: InChI=1S/C3H7NO/c1-4(2)3-5/h3H,1-2H3
The InChI Key is: ZMXDDKWLCZADIW-UHFFFAOYSA-N

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