chapter 3- chirality and stereoisomers

fischer projection

2D representation of a molecule - groups in front = horizontal line - groups in rear = vertical line (r and v look alike --> rear and vertical)

maximum number of stereoisomers

2^n; n= chiral centers

plane of symmetry

imaginary plane THROUGH an object

configurational isomers

isomers that can only interconvert if the bonds of the substituents were broken to create the other stereoisomers

molecules with symmetry and chiral center

look for plane of symmetry! might be meso--> less than max stereoisomers

superimposable

mirror molecules can be stacked up in a way that all of their components match up

enantiomers

stereoisomers that are nonsuperimposable mirror images; have opposite configurations at ALL chiral centers - chiral - one molecule will be R and other will be S - specific to molecules and there relationship

diastereomers

stereoisomers that are nonsuperimposable non-mirror images; have opposite configurations at SOME chiral centers - are stereoisomers that aren't enantiomers - will get RR and RS and vise versa

chiral center

tetrahedral atom/ SP3 atom that is bonded to FOUR different groups (usually a carbon)

stereoisomer

the same structural formula (constitutional isomers), atoms arranged differently in space - cis: substituents are on the same side and trans: different side

nonsuperimposable

when mirror images of organic molecules cannot be completely matched

chiral

a molecule that is not superimposable on its mirror image; can be present without chiral centers through conformational isomerism

stereocenter

an atom, most commonly carbon, about which exchange of two groups produces a different stereoisomer

mirror plane

between two molecules and gives you the mirror of each

meso compounds

certain molecules with two or more chiral centers that have fewer stereoisomers than maximum - end up getting a pair of enantiomers and the other "pair" is the same molecule --> not chiral due to symmetry (plane of symmetry) - one molecule is MESO; can have an enantiomer but it will be the same --> only draw one! - happens when you have two chiral centers that have the same 4 groups and are SR/RS

difference between chiral and enantiomers

chirality refers to objects- more broad and a single molecule can be chiral VS enantiomers refer to the relationship between a pair of objects - ex: this molecule is chiral and these two molecules are enantiomers - both have a mirror image that is nonsuperimposable

naming chiral centers

1) each atom bonded to a chiral center is assigned a priority; based off atomic number; highest atomic number --> highest priority (1) - if there is a tie look at what it is directly attached to and assign priority - if there is a double or triple bond- considered to be single bonded to that atom x times - always going to play your best card 2) orient molecule so the group of lowest priority is directed away from you 3) read the groups 1-2-3 4) if you read clockwise = R and counterclockwise = S

three types of assigning priority

1) lowest group already in the back--> read as is 2) lowest group is towards you--> opposite of what you see 3) lowest group is on the plane of the paper--> look down C-H bond OR rotate the dash, lowest group and wedge to get lowest group in the back

achiral

A molecule that is superimposable on its mirror image - has a plane of symmetry or center of symmetry

conformational isomers

Can be interconverted by free rotation about sigma bonds

drawing enantiomers and diastereomers

enantiomers - one chiral center: swap any two groups; S and R - two chiral centers: need to swap any two groups on ALL centers (R--> S)- RR and SS or RS and SR diastereomers - when n chiral centers exist: swap two groups on any number of the chiral centers less than n (centers are not inverted); RR and RS (only one group switched/was mirrored)