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Dimethyl Sulfoxide (DMSO)

Dimethyl sulfoxide (DMSO) is a polar aprotic solvent used often in Organic Chemistry. Its Lewis structure is a good example for formal charges, resonance, and how charge distribution affects reactivity.

Last updated July 2026•Fiveable Content Team

What is Dimethyl Sulfoxide (DMSO)?

Dimethyl sulfoxide, or DMSO, is a sulfur-containing organic solvent with the formula (CH3)2SO. In Organic Chemistry, you usually meet it as a polar aprotic solvent and as a clean example for checking formal charges in a Lewis structure.

The structure is simple to draw, but the charge pattern takes a little care. Sulfur is the central atom, bonded to two methyl groups and double-bonded to oxygen in one common Lewis structure. That arrangement gives sulfur a formal charge of 0, while oxygen also has a formal charge of 0, even though the molecule still has strong partial charges.

That is the part many people miss: formal charge and partial charge are not the same thing. DMSO has a strongly polarized S=O bond, so oxygen pulls electron density toward itself and becomes partially negative, while sulfur is partially positive. The molecule is neutral overall, but its electron distribution is uneven.

Resonance is how you explain that uneven distribution more completely. You can draw a second valid Lewis structure with sulfur single-bonded to oxygen and formal charges separated, or you can keep the neutral double-bond form. The real molecule is a resonance hybrid, which is why the S-O bond has characteristics in between a simple single bond and a pure double bond.

In class, DMSO shows up when you are thinking about solvent choice and structure together. It dissolves many polar and ionic organic compounds because it is very polar, but it does not donate hydrogen bonds the way water or alcohols do. That makes it especially useful when you want a polar environment without strongly tying up the nucleophile or reactant.

So if you see DMSO on a problem, ask two questions right away: what do the formal charges look like in the Lewis structure, and how does its polarity affect the reaction or solubility situation you are analyzing?

Why Dimethyl Sulfoxide (DMSO) matters in Organic Chemistry

DMSO matters in Organic Chemistry because it connects three ideas you use over and over: formal charge, resonance, and solvent effects. A lot of molecules can be drawn in more than one valid Lewis structure, but DMSO is a compact example where the formal charge bookkeeping and the actual electron distribution do not look identical at first glance.

That makes it a useful check on your understanding. If you can explain why sulfur can have formal charge 0 while the molecule is still highly polar, you are doing more than memorizing a structure. You are showing that you can separate formal charge from electronegativity and partial charge, which is a common source of mistakes on problem sets and quizzes.

DMSO also shows up as a solvent choice in reaction problems. Because it is polar aprotic, it can change how nucleophiles behave and can affect reaction rates compared with a protic solvent like water or methanol. Even when your course is not diving deep into mechanism yet, DMSO is a clue that the instructor wants you to think about solubility, polarity, and reactivity together.

On structure questions, DMSO is a good example for comparing Lewis structures, resonance forms, and electron domains around sulfur. On mechanism questions, it helps you remember that the reaction medium is not just background, it can shape the path a reaction takes.

Keep studying Organic Chemistry Unit 2

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How Dimethyl Sulfoxide (DMSO) connects across the course

Formal Charge

DMSO is a classic practice molecule for formal charge because you can calculate it on sulfur and oxygen without a huge structure getting in the way. The neutral Lewis structure is a good reminder that formal charge is a counting tool, not the same thing as where electron density actually sits in the molecule.

Resonance

The S-O bonding in DMSO is often explained with resonance because more than one Lewis structure can be drawn. The resonance idea helps you see why the sulfur-oxygen bond is highly polarized and why neither drawing by itself captures the whole picture.

Electronegativity

Oxygen is more electronegative than sulfur, so it pulls electron density toward itself in DMSO. That difference explains the partial negative charge near oxygen and the partial positive character near sulfur, even though the molecule has no net charge.

Nucleophilic

DMSO often appears in reactions involving nucleophiles because it is polar aprotic. That solvent environment can keep nucleophiles more reactive than they would be in a protic solvent, which changes how you predict reaction outcomes in mechanism problems.

Is Dimethyl Sulfoxide (DMSO) on the Organic Chemistry exam?

A quiz question might show you the DMSO Lewis structure and ask for formal charges, resonance forms, or the polarity of the molecule. In a reaction problem, you may need to notice that DMSO is the solvent and use that clue to reason about nucleophile behavior or solubility. If you are comparing structures, DMSO is also a quick check that you can separate formal charge from partial charge. On a short answer or mechanism item, naming DMSO as a polar aprotic solvent can be the difference between a guess and a solid explanation.

Dimethyl Sulfoxide (DMSO) vs Dimethyl Sulfone

DMSO is dimethyl sulfoxide, which contains sulfur bonded to oxygen in an S=O arrangement and is widely used as a solvent. Dimethyl sulfone is a different sulfur compound with two oxygens attached to sulfur and a very different oxidation state and reactivity profile. They sound similar, but they are not interchangeable in structure or function.

Key things to remember about Dimethyl Sulfoxide (DMSO)

  • Dimethyl sulfoxide (DMSO) is a polar aprotic solvent with the formula (CH3)2SO.

  • Its Lewis structure is a good example of how formal charge can be 0 even when the molecule is strongly polarized.

  • The sulfur-oxygen bonding in DMSO is explained with resonance and electronegativity, not just one fixed drawing.

  • Because DMSO is polar aprotic, it often changes how reactions and nucleophiles behave.

  • If you see DMSO in a problem, think structure, solvent effects, and electron distribution at the same time.

Frequently asked questions about Dimethyl Sulfoxide (DMSO)

What is Dimethyl Sulfoxide (DMSO) in Organic Chemistry?

Dimethyl sulfoxide, or DMSO, is a sulfur-containing compound used as a polar aprotic solvent in Organic Chemistry. It is also a useful molecule for practicing formal charge because its Lewis structure has a neutral overall charge but very uneven electron distribution.

Why does DMSO have formal charge 0?

In the common Lewis structure, sulfur and oxygen can each be assigned formal charge 0 when you count bonding and lone pair electrons correctly. Even with zero formal charge, the molecule is still highly polar because oxygen is more electronegative than sulfur and pulls electron density toward itself.

Is DMSO polar or nonpolar?

DMSO is polar. The S=O bond is strongly polarized, so the molecule has a large dipole moment even though it is neutral overall. That is why it dissolves many polar compounds and works differently from nonpolar solvents like hexane.

Why is DMSO a polar aprotic solvent?

DMSO is polar because of its uneven charge distribution, but it is aprotic because it does not have an O-H or N-H bond to donate a hydrogen bond. That combination makes it especially useful in reaction conditions where you want polarity without a protic solvent environment.