Chemistry / organic chemistry 1
SN2 reaction viewer
Follow nucleophilic substitution in 3D and see how bond changes invert the geometry at carbon.
SN2 reaction model
(S)-2-bromobutane
Progress shows an illustrative sequence, not elapsed reaction time.
The reaction is held at the question’s starting point, with product and mechanism answers hidden until you check.
Go to the question ↓This puts the nucleophile on the Br side of carbon. Select Backside to follow the SN2 pathway.
Bond changes and electron flow
Two electron pairs moveArrows show electron-pair movement from the reactants; they do not show atom trajectories.
Attack direction
Approach opposite Br
Use the frontside comparison to locate the incoming group relative to Br. In the SN2 pathway, the nucleophile and leaving group lie on opposite sides of the reacting carbon.
Transition state
Inspect the partial bonds
At the central stop, the incoming and outgoing bonds are both partial, while the three retained groups lie in a plane. This is a transition state within one concerted step, rather than a carbocation intermediate.
Stereochemistry
Track the retained groups
The three retained groups move from one side of their plane to the other. Compare the two 2-bromobutane enantiomers to see the inverted product configuration.
Try it yourself
SN2 prediction practice
Load a question, rotate the structure to inspect it, and predict the result before revealing the mechanism.
Load this question to begin.
The chemistry
How substitution changes stereochemistry
SN2 joins a nucleophile to carbon as the leaving group departs with the old bond’s electron pair. The geometry at carbon inverts during this process.
Bromomethane has three identical hydrogen substituents, so it has no R/S configuration before or after substitution. Each 2-bromobutane example has one stereocenter, whose configuration inverts in the illustrated SN2 pathway.
Explore the Newman projection viewer →Inversion and R/S labels
R/S describes the spatial arrangement after ranking the four groups by CIP priority. For the examples here, Br, O, or I ranks ahead of ethyl, methyl, and hydrogen, so inversion changes S to R or R to S. Recalculate priorities for other reactions instead of assuming the label must always change.
What controls a real reaction?
Substrate crowding, nucleophile, leaving group, and solvent affect SN2 reactivity. The animation follows a chosen pathway and does not compare reaction rates or competing elimination pathways.
Model assumptions and chemistry sources
The model interpolates idealized geometry along a single axis. Its reactant and product centers are tetrahedral; at the central stop, the retained groups are coplanar. Intermediate shapes and distances are illustrative and are not optimized molecular structures. The midpoint is an idealized transition-state representation, not a computed saddle point.
Each sphere labeled CH₃, C₂H₅, or OH represents that entire group; internal bonds and hydrogens are omitted. Colors identify roles rather than standard element colors. Approximate endpoint distances are C–H 1.09 Å, C–C 1.54 Å, C–O 1.43 Å, C–Br 1.94 Å, and C–I 2.14 Å. Partial-bond dashes and δ− labels are qualitative, not bond-order or charge calculations.
Reactants carry a −1 nucleophile and neutral alkyl bromide; products have a neutral substituted molecule and Br⁻, preserving total charge. The two curved arrows always depict electron flow starting from the reactants. The animation does not calculate activation energy, rate constants, solvent effects, or product mixtures, and playback duration does not represent physical time.
Background: John McMurry, Organic Chemistry, OpenStax, the SN2 mechanism, factors affecting SN2 reactions, and CIP sequence rules.