Stereoisomers (Ochem_chap5) Flashcards

2870716354	constitutional isomerism	compounds with identical molecular formulas but differ in order in which the individual atoms are connected	0
2870724114	Isomers		1
2870724115	stereoisomerism	isomers whose atoms are connected in the same order but differ in their spatial arrangement examples include (1) relatively stable and isolable cis-trans isomers (2) the rapidly equilibrating (and usually not isolable) conformational ones -cis/trans, anti/gauche, equatorial/axial, mirror-image stereoisomerism	2
2870742522	chiral	a molecule that is not superimposable on tis mirror image -molecules with one stereo center are always chiral -many chiral objects do not have stereo centers -only criterion for chirality is the non superimposable nature of object and mirror image	3
2870746960	enantiomer	each isomer of the image-mirror image pair	4
2870763228	test for chirality	the presence of absence of a plane of symmetry (mirror plane)-- one that bisects the molecule so that the part of the structure lying on one side of the plane mirrors the part on the other side chiral molecules cannot have a plan of symmetry	5
2870770336	optical activity of enantiomers	-special interaction with light: optical activity -enantiomers are frequently called optical isomers -when plane-polarized light is passed through a sample of one of the enantiomers, the plan of polarization of the incoming light is rotated in one direction (either clockwise or counterclockwise)	6
2870773068	dextrorotatory	-(dexter, Latin, right) -an enantiomer that rotates the plane of light in a clockwise sense as the viewer faces the light source -referred to as the (+) enantiomer	7
2870774422	levorotatory	-laevus, Latin, left -counterclockwise rotation -(-) enantiomer	8
2870777423	ordinary light and plane-polarized light	-bundles of electromagnetic waves that oscillate simultaneously in all planes perpendicular to the direction of the light beam -when such light is passed through a material called a polarizer, all but one of these light waves are "filtered" away, and the resulting beam oscillates in only one plane: plane-polarized light	9
2870803664	optical rotation	-when light travels through a molecule, the electrons around the nuclei and in the various bonds interact with the electric field of the light beam. -If a beam of plane-polarized light is passed through a chiral substance, the electric field interacts differently with, say, the "left" and "right" halves of the molecule -this interaction results in a rotation of the plane of polarization is called optical rotation -the sample giving rise to it is referred to as optically active	10
2870805895	polarimeter	optical rotations are measured by using a polarimeter	11
2870811074	racemic mixture (racemate)	a compound containing one stereo center is chiral and exists as a pair of enantiomers -A 1:1 mixture of enantiomers	12
2870816599	Absolute configuration: R-S sequence rules	-there is no straightforward correlation between the sign of rotation and the structure of the particular enantiomer -x-ray diffraction can establish the absolute configuration	13
2870831228	stereocenters are labeled R or S	-rank all four substituents in the order of decreasing priority -place the lowest-priority substituent farthest -if the progression from a to b to c is counterclockwise, the configuration at the stereocenter is named S (sinister, Latin, left) -if the progression is clockwise, the center is R (rectus, Latin, right) ex: (R)-2-bromobutane and (S)-2-bromobutanee the sign of the rotation of plane-polarized light maybe added if it is known, i.e. (S)-(+)-2-bromobutane and (R)-(-)-2-bromobutane	14
2870858677	sequence rules assign priorities to substituents	(1) look at atoms directly attached to the stereocenter. Higher atomic number has higher priority. In regard to isotopes, the atom of higher atomic mass receives higher priority (2) look for the first point of difference (3) double and triple bonds are treated as if they were single, and the atoms in them are duplicated or triplicated at each end by the respective atoms at the other end of the multiple bond.	15
2870878009	Fischer projection	simplified way of depicting tetrahedral carbon atoms and their substituents in two dimensions	16
2870899416	conversion of hawed-wedged line structures into fischer projections		17
2870902935	Fischer projections tell us the absolute configuration		18
2870906416	diastereomers	-presence of more than one stereocenter stereoisomers that are not related to each other as object to mirror image. -Cis and trans isomers of cyclic compounds are examples of disastereomers -because they are not mirror images of each other, diastereomers are molecules with different physical and chemical properties -a compound with n stereocenters can have a maximum of 2^n stereoisomers	19
2870971364	meso compound	a compound that contains two stereocenters but is superimposable with its mirror image (mess, Greek, middle) -the presence of an internal mirror plane	20
2871091978	In general, the formation of chiral compounds (e.g., 2-bromobutane) from chiral reactants (e.g., butane and bromine) yields	racemates. Or, optically inactive starting materials furnish optically inactive products	21
2871095756	stereoselective	the preference for the formation of one stereoisomer, when several are possible	22
2871096027	resolution	the separation of enantiomers -It is achieved by the reaction of the racemate with the pure enantiomer of a chiral compound to yield separable diastereomers -chemical removal of the chiral reagent frees both enantiomers of the original racemate.	23
2871098396	chiral chromatography	another way of separating enantiomers is by chiral chromatography on an optically active support -the sample is applied to the top of a column filled with an enantiopure chiral support. One enantiomer (green) interacts more strongly with the support than the other (red) and is relatively slow to pass through the column -the red enantiomer is eluted before its green mirror image. Commercial columns often use the glucose polymer cellulose as the chiral stationary phase.	24