Stereochem_Primer

Stereochem_Primer - 1. Visualization Skills 2. Chirality...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
1. Visualization Skills 2. Chirality and Enantiomers 3. Diastereomers 4. Finding Meso 1. Visualization Skills Proper use of stereochemical concepts requires an ability to perceive 3-dimensional objects rendered on a two dimensional sheet of paper or a board. You need to be able to “see” how rotating a molecule in space changes the positions of groups around a stereocenter. You also need to “see” how reflecting a molecule in a mirror plane changes the relative positions of groups around a stereocenter . A stereocenter (also called a chiral center or stereogenic center) is an atom connected to four different groups. Rotate a molecule about an axis - changes the molecule’s orientation. Rotation about an axis does not change a molecule’s shape, conformation or any stereocenter’s configuration. CONVINCE YOURSELF THAT - ALL 3 ROTATED STRUCTURES ARE THE SAME AS THE OBJECT Reflection a molecule in a plane – not a physically achievable motion (try to convert your left hand into your right hand ). Reflection changes every stereocenter’s configuration. CONVINCE YOURSELF THAT - ALL 3 REFLECTED STRUCTURES ARE THE SAME - ALL 3 REFLECTED STRUCTURES ARE NOT SUPERIMPOSABLE ON THE OBJECT CD AB DC reflection in vertical plane perpendicular to the page object reflection object reflection reflection in plane defined by the page BA object reflection reflection in horizontal plane perpendicular to the page rotate about a vertical axis in the page object rotated object rotated rotate about a horizontal axis in the page object rotated rotate about an axis perpendicular to the page
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2. Chirality and Enantiomers A chiral entity is not superimposable on its mirror image . The above object and its reflection are chiral. Neither is superimposable on the other (its mirror image). The above molecule (object) and its reflection are one example of stereoisomers . Two molecules are stereoisomers if they have the same composition, constitution and connectivity but different 3-dimensional shapes that cannot be superimposed in any conformation without breaking bonds. There are two main classes of stereoisomers: enantiomers and diastereomers . Enantiomers: two molecules are enantiomers if they are stereoisomers and mirror images . (Alternate definition: two molecules are enantiomers if they have the same connectivity, are mirror images but are non-superimposable). object reflection 180 rotation rotated reflection Starting with the object [ (R)-3-methylheptane ], reflection in the plane generates a new structure (reflection). A 180 o rotation about a vertical axis generates the rotated reflection. Although the heptane chain of the object and the rotated reflection can be perfectly overlayed, the 3-CH 3 group of the object points toward the viewer whereas the 3-CH 3 group of the rotated reflection [ (S)-3-methylheptane ], points away from the viewer. The third carbon is a stereocenter.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 7

Stereochem_Primer - 1. Visualization Skills 2. Chirality...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online