Isotoon explains organic chemistry in three dimensions. Ask about a mechanism, SN1 versus SN2, or a chiral center and get an animated walkthrough, or a 3D model of the molecule you can rotate and step through.
Organic chemistry is a three-dimensional subject taught on flat paper. Ask about a mechanism or a chiral center and turn the molecule around until it makes sense.
In an SN2 reaction the nucleophile attacks the carbon from the side opposite the leaving group, and the new bond forms as the old one breaks, in a single step. Because the attack comes from behind, the other three groups flip over like an umbrella in the wind, inverting the stereocenter. The rate depends on both the substrate and the nucleophile, and crowded tertiary carbons block the approach.
An SN1 reaction takes two steps: the leaving group leaves first, giving a flat carbocation, and the nucleophile then adds to either face of it. That is why SN1 tends to give a mix of both configurations. It is favored by tertiary carbons, which stabilize the carbocation, by weak nucleophiles, and by polar protic solvents such as water and alcohols.
A molecule is chiral when it cannot be superimposed on its mirror image, the way a left hand cannot be laid exactly over a right one. The usual cause is a carbon bonded to four different groups, called a stereocenter. The two mirror-image forms, enantiomers, share boiling points and most other properties, but they rotate plane-polarized light in opposite directions and can act very differently in the body.
The ones marked 3D become a model you can turn, step through and tap.
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