MO4 Bonding And Stereochemistry Flashcards
Define stereochemistry
The 3D arrangement of atoms in molecules and how this arrangement affects chemical behaviour and properties. How different possible orientations of atoms/groups within a molecule influence its interactions, reactivity, and biological activity.
Explain term enantiomer
A chiral molecule and its mirror image are enantiomers. Enantiomers have very different biological activity but the same physical properties. They interact with a plane of polarised light in a different way, rotating in equal but opposite directions.
Explain term diastereomer
Similar to enantiomers but have more than one chiral centre and are NOT mirror images of each other. Usually have different biological and physical properties. Usually optically active rotating plane polarised light but this is not necessarily in an equal and opposite direction.
- non superimposable and are not mirror images of each other.
- 2 or more chiral centres
-different but similar physical properties - often have different biological activities
- still optically active (rotate plane polarised light) but for a pair of diastereoisomers this is not always in equal and opposite direction
Explain term geometric isomer
- different 3D arrangement is at the double bond
- different physical properties
- can have different biological properties
- not superimposable
Explain term chiral
- Cannot be superimposed on their own mirror image.
- does not have a plane of symmetry
Explain term chiral centre
- commonly a tetrahedral carbon atom, C with 4 different groups attached\
Explain the term specific rotation
The amount of rotation of plane - polarised light per unit conc and path length
Explain the term optical activity
The ability of a substance to rotate the plane of polarisation of a beam of light that is passed through it.
Explain the term racemic mixture/racemate
A mixture containing equal amounts of two enantiomers resulting in an optically inactive solution because it cancels out when each enantiomer rotates equally in opposite directions.
What are the R and S nomenclature e
For naming enantiomers using the substituents around a chiral centre. The higher the atomic number of the atom directly attached to the chiral C, the higher the priority assigned. The lowest priority points towards the back (away from you) and the remaining 3 either go in a clockwise (R) or anticlockwise) direction
What are the D and L nomenclature
Old way to classify a chiral centre. Does NOT tell you R or S and is different to (+)dextrotatory and (-)levorotatory.
What does (+) and (-) nomenclature mean
- (+)= dextrorotatory, rotates to the right
- (-)= levorotary, rotates to the left
Explain the E and Z nomenclature
Describes the orientation for a geometric isomer which is around a double bond.
- For each side of the bond the highest atomic number is identified.
- if on same side = Z
- if on opposite sides = E
What creates bonds between atoms?
The arrangement of electrons. The valence (outer shell) electrons participate in bonding with the goal of completing their outer shell to have 8 electrons.
What are the different types of chemical bonds?
- Ionic = one atom transfers electrons to another atom to give an anion and a cation. Electrons are not shared. Held together by attraction of opposite charges (electrostatic interaction).
- covalent (non polar, electrons sit in the middle and polar, electrons sit closer to the more electronegative of the bond) = 2 atoms share electrons (‘bonding electrons’). When polar, a dipole is created which gives rise to reactivity and intermolecular interactions
How many bonds do each C, N , O and H have
C=4
N=3
O=2
H=1
What are the two strongest intermolecular forces
- dipole-dipole interactions = ‘two poles’, separation of partial charges creates a dipole. Partial charges of one molecule are attracted to an opposite partial charge in a nearby molecule. Much weaker than ionic or covalent bonds.
- hydrogen bonds = special type of dipole- dipole interaction, stronger than non-H dipole-dipole interactions. Each partner in the H - bond has polar covalent bond, eg RO-H, RN-H, F-H (not C-H as not polarised enough). Intramolecular H bonds can form in some molecules.
