Chirality Flashcards
How can chiral molecules be distinguished
Through their interactions with other chiral molecules
Types of axes of symmetry
n-fold. 2 fold is between bonds, 3 fold is along a bond
Symmetry of benzene
7 planes of symmetry, 6 2-fold axes and a 6-fold axis
General number of stereoisomers rule
2^n where n is the number of chiral centres
Fischer projections
Cross-like representation. vertical = out of the page, horizontal = into from the page (solid)
Under what circumstances is a biaryl chiral
when there is restricted rotation about the Ph-Ph bond and no symmetry
Structure of allenes
A 1,2 diene. The substituents of the terminal carbons are perpendicular to each other, and the lack of flexibility in the structure means that as long as there are R substituents, it will be chiral
Chirality of phosphines vs amines
Amines readily invert their structure and so exist as both enantiomers. Phosphines do not readily invert and so exist as a single enantiomer
Conformers
Energy minima of geometries of molecules that arise through rotation about free bonds
What is the dihedral/torsion angle
The angle between substituents. Best measured in a Newman projection
Dihedral angles of eclipsed structures
0, 120 and 240
Dihedral angles when substituents are staggered
60, 180 and 300
Orbital overlap in eclipsed and staggered conformations
In eclipsed conformations, there is overlap between filled bonding orbitals which raises the energy of the system. In staggered conformations, there is overlap between the bonding and anti-bonding orbitals of adjacent substituents which stabilises the structure.
Energy difference between eclipsed and staggered structures in ethane
12 kJmol-1
Populations of gauche and anti-periplanar conformations equation
K = [anti]/[gauche] = exp(-dG/RT)
