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51 Cards in this Set
- Front
- Back
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structural isomers = constitutional isomers...
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have the same molecular formula..though different structures
-each variation has different physical and chemical properties |
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physical properties
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melting point
boiling point solubility -determined by intermolecular forces |
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chemical properties
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things that determine how the molecule reacts with other molecules
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stereoisomers
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have the same chemical formula
-like isomers |
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difference between stereoisomers?
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arrangement in space
= geometric, enantiomers, diastereomers, meso compounds, conformational isomers |
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geometric isomers
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compounds that differ in position of substituents attached to a double bond or cycloalkane
aka cis and trans arrangements |
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cis arrangement
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both substituents are on the same side of the double bond
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trans arrangement
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substituents are on opposite sides of the double bond
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cis = Z
trans = E |
know
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chirality
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when an object is non-superimposable upon its mirror image
also has 4 separate/different substituents |
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achiral
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objects that can be fit onto their mirror images
-have a plane of symmetry -no optical activity |
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enantiomers
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non-superimposable mirror images
-chiral centers that are opposite in direction! |
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true/false: rotating a molecule changes its chirality
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false
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configuration =
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spatial arrangement of the atoms/groups of a stereoisomer
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relative configuration
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-configuration in relations to another chiral molecule (does it have higher priority in relations to what surrounds it?)
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absolute configuration
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R or S configuration
based off priority order R = clockwise S = counterclockwise |
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fischer projections
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horizontal atoms point outward
veritcal atoms point away/downward |
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a compound is optically active if it has the ability to rotate plan-polarized light
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know
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a compound that rotates the plane of polarized light to the right (CW) is dextrorotary and +
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know
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a compound that rotates the plane of polarized light to the left(CCW) is levorotary and (-)
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know
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direction of rotation is/is not related to absolute configuration of the molecule
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is not
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amount of rotation depends on two things...
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1. concentration of optically active compound(enantiomer)
2. length of the tube through which the light passes |
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specific rotation[ἀ] =
observed rotation(ἀ) divided by [(concentration(g/mL))*(length(dm))] ἀ = alpha |
know
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racemic mixture
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when both + and - enantiomers are in equal concentrations
rotations of both cancel one another out and no optical activity is observed |
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diastereomers
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non-mirror configurational isomers
-do not have opposite absolute configurations like enantiomers -required to have more than 2 chiral centers |
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molecule with n chiral centers means there a potentially 2^n configurations
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know
ex) 3 chiral centers = 9 potentials... RSR RSS RRS RRR SSS SSR SRR SRS ??? |
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RR's mirror image is
RS's mirror image is |
SS (enantiomers)
SR (enantiomers) however, SS and SR are diastereomers |
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meso compounds
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have a plane of symmetry
not optically active can have chiral centers |
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conformational isomerism
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are the same molecules, only at different points of rotation in space
single bonds can rotate while double bonds can not |
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newman projection is circular drawing
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know
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newman projection arrangements of atoms in relations to one another (4 types)
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staggered
gauche eclipsed anti |
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staggered arrangement
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when all molecules in drawing are at 60degree angles to one another...least straining arrangement
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anti arrangement
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variation of staggered
-when methyl groups are 180 degrees from one another = antiperiplanar arrangement |
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gauche arrangement
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staggered formation type
-occurs when methyl groups are within 60degrees of one another |
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eclipsed arrangement
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when molecules overlap one another...very strainful
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total eclipse arrangement
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eclipse variation
-occurs when two methyls overlap one another |
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RR's mirror image is
RS's mirror image is |
SS (enantiomers)
SR (enantiomers) however, SS and SR are diastereomers |
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meso compounds
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have a plane of symmetry
not optically active can have chiral centers |
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conformational isomerism
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are the same molecules, only at different points of rotation in space
single bonds can rotate while double bonds can not |
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newman projection is circular drawing
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know
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newman projection arrangements of atoms in relations to one another (4 types)
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staggered
gauche eclipsed anti |
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cyclic conformations and ring strain (3)
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1. angle strain
2. torsional strain 3. nonbonded strain |
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angle strain
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results when bond angles deviate from their ideal values
-become larger/smaller in angle |
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torsional strain
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results when cyclic molecules must assume conformations that have eclipsed interactions
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nonbonded strain
aka steric strain |
aka van der waals repulsion
-results when nonadjacent atoms or groups compete for space ex) two CH3 molecules within 60 degrees of one another have a chance of hitting one another while in space/rotation |
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to alleviate strainl;
-cyclobutane will form a V -cyclopentane will form envelope |
know
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cyclohexane
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can form
-boat -chair twist |
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cyclohexane unsubstituted
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most stable form = chair
--all three strains eliminated in this shape |
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axial arrangement
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when molecules point up/down
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equitorial arrangement
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when molecules point horizontally
-most preferred for bulky substituents |
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boat flip
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asdasd
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