Unit 2 Textbook Notes
Chapter 6
• Low in energy positions (confirmations) are easier to do than high in energy ones
• Some reactions can only happen in specific conformations
• Newman projections
o
o The circle parts are also carbons
o Eclipsed: covered
o
• Single bonds freely rotate
• Anti conformation: most stable rotation
• Gauche conformation: slightly less stable and steric (crowded)
• Chair projections
o
o Draw axial substituents up and down at each carbon
§
o Draw equatorial substituents outwards at each carbon, parallel to the bond on
which it is drawn
, §
o Draw H at the end of the lines or else it implies methyl group
o Wedge goes up, dash goes down
o Hexagon is the same as a chair
§ Any numbering is fine but you must go the same direction as the hexagon
o Trans is when one group is on a wedge, one on a dash
§ Cis is both dashes or both wedges
o Ring flipping
§ Equatorial positions switch to axial and vice versa
§ Constantly flipping
§ Up/down flip does not change
•
§ Any hexagon has two chair confirmations
• Axial or equatorial
o Stability of Chairs
§ E2 reactions can only proceed if a certain group is in axial positions
§ Unstable rings do not equally flip
§ More stable with a group in an equatorial position
• Less steric interaction
§ Larger groups prefer to be equatorial
Chapter 7
• Configurations cannot change without a chemical reaction
o Like no matter how your hand moves, it’s still the same hand overall
• Conformation: different positions a molecule can twist into
o Confirmational isomers are identical
• Configuration: right-handedness (R) or left-handedness (S)
• Optically inactive includes achiral or chiral racemic
• R or S are stereocenters/chiral centers
o Some reactions can change R to S or vice versa
o Stereocenter: the carbon atom with four different groups attached
o Stereocenters do not have CH2 groups
• Finding Configuration
o R or S
o Number all groups 1-4
, § Highest atomic number is has priority
• If multiple carbons, list all atoms to which the carbon is attached
besides stereocenter and use atomic number rule again on the
first difference
• So if there’s a CH3 and a CCH, CCH comes first bc another carbon
• If the same, keep going outwards until there is a difference
§ Hydrogen always comes last
§ Double bond counts as connection to 2 carbons
o Clockwise is R, counterclockwise is S
§ If 4 is on a dash, just look at 1, 2, 3
§ If not, rotate until 4 is on a dash then look at 1, 2, 3
• If you redraw the molecule so any 2/4 groups are switched, R
turns to S and vice versa
• Nomenclature
o If only one stereocenter, put R or S at the beginning of the nomenclature
o If multiple stereocenters, put location of each stereocenter
o Italicize
§ Ex: (3R, 4S)
§
o Cannot use cis/trans if four different groups on a double bond bc two possible
stereoisomers
§ Look at both sides of the double bond and find priority with the four
groups
• Enantiomers
o Having enantiomer means chiral
§ But not all chiral molecules have enantiomers
§ Wedge and dash means chiral
o Cannot be superimposed
o Can only be distinguished in chiral environments
o Always come in pairs
o Redraw carbon skeleton but change all dashes into wedges and vice versa
§
o Inversion of all stereocenters
o If no dashes or wedges
Chapter 6
• Low in energy positions (confirmations) are easier to do than high in energy ones
• Some reactions can only happen in specific conformations
• Newman projections
o
o The circle parts are also carbons
o Eclipsed: covered
o
• Single bonds freely rotate
• Anti conformation: most stable rotation
• Gauche conformation: slightly less stable and steric (crowded)
• Chair projections
o
o Draw axial substituents up and down at each carbon
§
o Draw equatorial substituents outwards at each carbon, parallel to the bond on
which it is drawn
, §
o Draw H at the end of the lines or else it implies methyl group
o Wedge goes up, dash goes down
o Hexagon is the same as a chair
§ Any numbering is fine but you must go the same direction as the hexagon
o Trans is when one group is on a wedge, one on a dash
§ Cis is both dashes or both wedges
o Ring flipping
§ Equatorial positions switch to axial and vice versa
§ Constantly flipping
§ Up/down flip does not change
•
§ Any hexagon has two chair confirmations
• Axial or equatorial
o Stability of Chairs
§ E2 reactions can only proceed if a certain group is in axial positions
§ Unstable rings do not equally flip
§ More stable with a group in an equatorial position
• Less steric interaction
§ Larger groups prefer to be equatorial
Chapter 7
• Configurations cannot change without a chemical reaction
o Like no matter how your hand moves, it’s still the same hand overall
• Conformation: different positions a molecule can twist into
o Confirmational isomers are identical
• Configuration: right-handedness (R) or left-handedness (S)
• Optically inactive includes achiral or chiral racemic
• R or S are stereocenters/chiral centers
o Some reactions can change R to S or vice versa
o Stereocenter: the carbon atom with four different groups attached
o Stereocenters do not have CH2 groups
• Finding Configuration
o R or S
o Number all groups 1-4
, § Highest atomic number is has priority
• If multiple carbons, list all atoms to which the carbon is attached
besides stereocenter and use atomic number rule again on the
first difference
• So if there’s a CH3 and a CCH, CCH comes first bc another carbon
• If the same, keep going outwards until there is a difference
§ Hydrogen always comes last
§ Double bond counts as connection to 2 carbons
o Clockwise is R, counterclockwise is S
§ If 4 is on a dash, just look at 1, 2, 3
§ If not, rotate until 4 is on a dash then look at 1, 2, 3
• If you redraw the molecule so any 2/4 groups are switched, R
turns to S and vice versa
• Nomenclature
o If only one stereocenter, put R or S at the beginning of the nomenclature
o If multiple stereocenters, put location of each stereocenter
o Italicize
§ Ex: (3R, 4S)
§
o Cannot use cis/trans if four different groups on a double bond bc two possible
stereoisomers
§ Look at both sides of the double bond and find priority with the four
groups
• Enantiomers
o Having enantiomer means chiral
§ But not all chiral molecules have enantiomers
§ Wedge and dash means chiral
o Cannot be superimposed
o Can only be distinguished in chiral environments
o Always come in pairs
o Redraw carbon skeleton but change all dashes into wedges and vice versa
§
o Inversion of all stereocenters
o If no dashes or wedges
