---
title: "Sulfoxide (R2SO) | Organic Chemistry"
description: "Sulfoxide (R2SO) is a sulfur compound with sulfur bonded to two carbon groups and one oxygen, formed by oxidizing a sulfide in Organic Chemistry."
canonical: "https://fiveable.me/organic-chem/key-terms/sulfoxide-r2so"
type: "key-term"
subject: "Organic Chemistry"
unit: "Unit 18"
---

# Sulfoxide (R2SO) | Organic Chemistry

## Definition

A sulfoxide (R2SO) is an organic sulfur compound where sulfur is bonded to two carbon groups and one oxygen atom. In Organic Chemistry, it shows up as an oxidation product of sulfides.

## What It Is

A sulfoxide is an organic sulfur compound with the general formula R2SO, meaning one sulfur atom is attached to two carbon-containing groups and one oxygen atom. In Organic Chemistry, that makes it a simple but important oxidation product of a sulfide, which has the formula R2S.

The big structural feature is the S=O bond. Chemists often draw it that way, but the real bonding is a polar sulfur-oxygen bond with some double-bond character rather than a perfectly ordinary carbonyl-style double bond. Because oxygen is much more electronegative than sulfur, the oxygen pulls electron density toward itself, so sulfoxides are strongly polarized molecules.

That polarity changes the way sulfoxides behave. The sulfur is not just a passive center, and the oxygen can act as a site for interactions with acids or reagents. At the same time, the two groups attached to sulfur can be different, so sulfoxides can exist in chiral forms when those groups are not identical. That is a nice stereochemistry detail that often surprises people the first time they see sulfur-centered chirality.

A common way to form a sulfoxide is controlled oxidation of a sulfide. Add one oxygen in the right conditions and you stop at the sulfoxide stage. If oxidation continues, you can go further to a sulfone, which has two oxygens on sulfur. So when you see a sulfoxide, think of it as the middle oxidation level between sulfide and sulfone, not just a random sulfur oxygen compound.

In practice, sulfoxides show up in reaction mechanisms, synthesis schemes, and naming questions. Dimethyl sulfoxide, or DMSO, is the most familiar example, but the term itself covers many R2SO structures. If you can spot sulfur, two carbon groups, and one oxygen, you are looking at a sulfoxide.

## Why It Matters

Sulfoxides matter because they sit right in the middle of sulfur oxidation chemistry, and that middle position often controls what happens next in a synthesis. If a problem gives you a sulfide, thiol-derived product, or oxidation reagent, recognizing a sulfoxide helps you track how many oxygens have been added and whether the reaction stopped at the right stage.

They also show up in structure and reactivity questions. The S=O bond makes sulfoxides more polar than sulfides, so they behave differently in solubility, intermolecular interactions, and reaction pathways. That polarity can affect how a molecule is isolated, purified, or discussed in a mechanism.

Sulfoxides are a useful checkpoint for oxidation state logic too. In organic chemistry, you are often asked to rank sulfur-containing compounds or describe the product of partial oxidation. Seeing R2SO tells you sulfur has been oxidized once compared with R2S, but not as far as a sulfone.

They also connect to stereochemistry. A sulfoxide can be chiral at sulfur when the two carbon groups are different, so it can appear in questions about stereoisomers, optical activity, or why a compound may have nonidentical mirror-image forms even without a chiral carbon.

## Connections

### Sulfides

Sulfoxides are the oxidation products of sulfides. If you start with R2S and add one oxygen, you get R2SO. That makes sulfides the best starting point for understanding where sulfoxides come from and how to tell whether a reaction has gone one oxidation step or more.

### Oxidation

The key reaction that forms a sulfoxide is oxidation of sulfur. In problem sets, this usually means tracking oxygen addition and comparing the starting sulfur compound to the product. Sulfoxides are a clear example of oxidation in organic chemistry because the sulfur center changes without needing a carbon skeleton rewrite.

### [Oxidation States of Sulfur](/organic-chem/key-terms/oxidation-states-sulfur)

Sulfoxides are useful for practicing sulfur oxidation state changes. Compared with sulfides, they represent a higher oxidation level, but they are not as oxidized as sulfones. That makes them a good middle-case molecule when you are asked to rank sulfur compounds or identify oxidation progression.

### [Disulfide](/organic-chem/key-terms/disulfide)

Disulfides and sulfoxides can both appear in sulfur chemistry, but they are not the same kind of functional group. A disulfide has an S-S bond, while a sulfoxide has an S=O unit. If you are tracing reaction products, the bond pattern tells you whether sulfur atoms are linked to each other or to oxygen.

## On the AP Exam

A quiz question might show a structure and ask you to name the functional group or predict the product of oxidizing a sulfide. The move is to identify sulfur bonded to two carbon groups and one oxygen, then label it as a sulfoxide rather than a sulfide or sulfone. If the prompt gives a reaction sequence, you may need to count oxidation steps and decide whether the reagent stopped at R2SO.

In mechanism or synthesis questions, you may also explain why the sulfoxide is more polar than the starting sulfide, or point out that sulfur can become a stereocenter when the two carbon groups differ. On structure comparison items, the fastest method is to check the oxygen count on sulfur and the bond pattern around it.

## sulfoxide (R2SO) vs Sulfides

Sulfides are R2S, with sulfur bonded to two carbon groups and no oxygen. Sulfoxides are the oxidized form, R2SO, so the presence of one oxygen is the quickest way to separate them. In organic chemistry problems, this distinction often tells you whether oxidation has already happened.

## Key Takeaways

- A sulfoxide is an organosulfur compound with formula R2SO, meaning sulfur is attached to two carbon groups and one oxygen.
- It is usually formed by partial oxidation of a sulfide, so it sits between sulfides and sulfones in sulfur oxidation chemistry.
- The S=O bond makes sulfoxides more polar than sulfides, which changes how they behave in reactions and physical properties.
- Sulfoxides can be chiral at sulfur when the two carbon groups are different, so stereochemistry can matter.
- When you see R2SO in a reaction or structure, the fastest question to ask is whether the compound came from oxidation of a sulfide.

## FAQs

### What is sulfoxide (R2SO) in Organic Chemistry?

A sulfoxide is an organic sulfur compound where sulfur is bonded to two carbon groups and one oxygen atom. In Organic Chemistry, it usually appears as the product of oxidizing a sulfide. The formula R2SO is the quick visual cue.

### How is a sulfoxide different from a sulfide?

A sulfide is R2S, so sulfur is bonded to two carbon groups and no oxygen. A sulfoxide is R2SO, which means one oxygen has been added by oxidation. That one oxygen changes the polarity and often the reactivity of the molecule.

### Is a sulfoxide the same as a sulfone?

No. A sulfoxide has one oxygen on sulfur, while a sulfone has two. If you are reading a structure, count the oxygens attached to sulfur to tell them apart. Sulfoxides are the partially oxidized form between sulfides and sulfones.

### Can sulfoxides be chiral?

Yes, a sulfoxide can be chiral at sulfur if the two carbon groups attached to sulfur are different. That comes up in stereochemistry because the sulfur center can act like a stereocenter. It is a common detail in more advanced structure questions.

## Related Study Guides

- [18.7 Thiols and Sulfides](/organic-chem/unit-18/thiols-sulfides/study-guide/wrb7uXOfoVYbwYT1)

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