4. Chapter 4 Flashcards
(12 cards)
What are isomers?
What are conformational and constitutional isomers?
Isomers- molecules with identical molecular formula but different structure
Conformational- sane molecular formula, same connectivity of atoms, only differ due to rotation about single bonds
Constitutional- same molecular formula but different connectivity between atoms
Slide 3
What are stereoisomers?
What are enantiomers and diastereomers?
Same molecular formula, same connectivity between atoms, but different 3D arrangement of atoms
Enantiomers- stereoisomers that are non-superimposable mirror images
They are chiral molecules
Diastereomers- non mirror images and non identical stereoisomers (have same configuration at 1 or more stereogenic centres, but differ at the remaining stereogenic centres)
Beside slide 26
Slides 27-30
What is chirality?
What is chiral and achiral?
What are chiral centres?
Chirality- ability of objects to exist as non-superimposable mirror images of each other
Chiral- objects aren’t not superimposable in their mirror image
Achiral- objects are superimposable on their mirror image
Slide 6-9
Chiral centres are atoms that are connected to 4 different groups
What are stereocentres or stereogenic centres?
Stereogenic centres- atoms for which the exchange of 2 substituents can produce a stereoisomer
Most often an atom connected to 4 different groups
Lone pairs don’t count as stereogenic
Slides 12-15
Can a molecule be achiral in the presence of stereogenic centres?
Yes
Meso compounds are a good example
A molecule can be chiral even in the absence of stereogenic centres as well
Slide 14
What are atropisomers?
Stereoisomers that result from hindered rotation around a single bond
Slide 15
What is the absolute configuration of a stereocentre?
What does R and S mean?
Describes the exact 3D arrangement of the atoms around a chirality centre
Each substituent attached to a stereo centre is assigned a priority based on atom directly attached to centre
Higher atomic number= higher priority
R- (rectus) means atoms turns clockwise is priority
S- (sinister) means atoms turn counterclockwise in priority
Slides 18-25
What is a meso compound?
Achiral molecule, is superimposable onto its own mirror image
Contain more than one stereocentre and have superposable mirror images
Slide 30
Page 158-159
What is the E or Z nomenclature for double-bond stereoisomers?
E double bond (entgegen) higher priority groups on each Carbon are on opposite sides of double bond
Z double bond (zusammnen “zee zame zide”)- higher priority groups of each Carbon are on same side of double bond
Slides 37-42
What are the physical properties of enantiomers?
They are physically and chemically identical
Same melting point, boiling point, chemical reactions, etc.
Behave differently when they interact with another chiral molecule (bodies made of mostly chiral molecules we interact differently with 2 enantiomers of chiral compounds) and plane polarized light
How do chiral molecules rotate the plane of polarized light?
Enantiomers rotate polarized light by the same magnitude, but opposite directions
Magnitude= α (specific rotation dependant on path length and sample concentration)
Dextrorotary (+ or d)- clockwise turn of light
Levotary (- or l)- counterclockwise turn of light
No relationship between R/S assignment and optical rotation
What is a racemic compound?
Mixture of equal amounts of both enantiomers of a compounds
Race mates do not rotate plane-polarized light
