Each C–Cl bond is strongly polarized (Cl is far more electronegative than C: χ = 3.16 vs 2.55). The two C–Cl dipoles point from C toward Cl. Due to the ~112° Cl–C–Cl angle, these two dipoles do not point in exactly opposite directions - their vector sum is nonzero, pointing toward the Cl₂ face of the molecule.

The two C–H bond dipoles (pointing from H toward C, as C is slightly more electronegative than H) also add a component in the same direction. The overall result: a net dipole moment of 1.60 D pointing toward the chlorine-bearing side.

Both Cl atoms pull σ-electron density toward themselves, creating a partial positive charge (δ+) on carbon. This makes the carbon slightly electrophilic - relevant to DCM's ability to act as a Lewis acid–like solvent in certain reactions and its affinity for nucleophilic substrates.

Chlorine's lone pairs can donate back into the C–Cl σ* antibonding orbital (negative hyperconjugation), partially compensating for the inductive withdrawal. This back-donation strengthens the C–Cl bond (relative to a purely inductive model) and contributes to DCM's chemical stability under ambient conditions.

With two electron-withdrawing Cl atoms adjacent to carbon, the C–H bonds in DCM are more acidic than those in alkanes (pKa ≈ 24 in DMSO vs ~50 for methane). This weak acidity enables DCM to act as a hydrogen bond donor in some systems - a subtle but measurable effect on solvation behavior.

Q1: What is the molecular formula of dichloromethane?

The molecular formula of dichloromethane is CH₂Cl₂. It consists of one carbon atom, two hydrogen atoms, and two chlorine atoms. The molecular weight is 84.93 g/mol. The SMILES notation is ClCCl and the CAS number is 75-09-2. The empirical formula is the same as the molecular formula since DCM is a small discrete molecule, not a polymer or extended structure.

Q2: What is the Lewis dot structure of DCM and how many lone pairs does it have?

The Lewis dot structure of DCM shows carbon at the center forming four single bonds - two to H and two to Cl. Carbon has no lone pairs (all four valence electrons are in bonding pairs). Each chlorine atom has three lone pairs (6 non-bonding electrons). Hydrogen has no lone pairs. In total the molecule has 6 lone pairs (12 non-bonding electrons) and 4 bonding pairs (8 bonding electrons), for 20 valence electrons total.

Q3: What is the molecular geometry of DCM?

DCM has a tetrahedral molecular geometry with C₂ᵥ symmetry. The carbon is sp³ hybridized with four bonding pairs and no lone pairs. The ideal tetrahedral angle is 109.5°, but the actual bond angles deviate slightly: Cl–C–Cl ≈ 111.8°, H–C–H ≈ 112.0°, and H–C–Cl ≈ 108.0°. These deviations arise from the greater steric size of chlorine relative to hydrogen.

Q4: Is DCM polar - and if so, why doesn't it mix with water?

DCM is a polar molecule (dipole moment 1.60 D), but it does not mix freely with water because it cannot donate hydrogen bonds. Water molecules hold together primarily through hydrogen bonding (O–H···O interactions). DCM has no O–H or N–H groups, so it cannot participate in these interactions as a donor. The energy cost of disrupting the water hydrogen-bond network to accommodate DCM molecules is too high - so two phases form. DCM does dissolve about 20 g/L in water because it can accept some hydrogen bonds through its chlorine lone pairs.

Q5: Does DCM have resonance structures?

No - DCM has a single Lewis structure with no resonance. Resonance requires delocalized π electrons (e.g., in benzene, carbonate ion, or acetate). DCM contains only single bonds (σ bonds) - there are no π bonds or adjacent lone pairs that could delocalize into an adjacent π system in a meaningful way. The formal charges on all atoms are zero in the single correct Lewis structure, confirming it is the complete and only valid representation.

Q6: How does DCM's structure explain its use as an extraction solvent?

Three structural features make DCM ideal for liquid–liquid extraction: (1) Its intermediate polarity (C₂ᵥ symmetry, 1.60 D) allows it to dissolve a wide range of organic compounds - both polar drugs/natural products and nonpolar fats/waxes. (2) Its high density (1.325 g/cm³, from the two heavy chlorine atoms) means it reliably settles to the bottom when mixed with aqueous solutions, giving a clear, easy phase separation. (3) Its low boiling point (39.6 °C, from its small molecular size) means the extracted product can be recovered by gentle evaporation without heat damage.