Structure 3.2 HL Flashcards
Isomers
Compounds of the same molecular formula that differ from each other in the arrangement of their atoms
Stereoiosmerism
Isomers with different arrangements of atoms in space that DO NOT differ in connectivity or bonding (single/double/triple)
Conformational isomers
Isomers that interconvert by rotation around a sigma bond (as it is a single bond, the atoms can move around the atom to change layout - remember molymod exercise in class)
Configurational isomers
Isomers that interconvert only by breaking and reforming a bond. (molymod exercise in class)
Cis-trans isomers
Cis bonds are when they are all on the same side (no rotation). Trans is when there has been a rotation
Physical and chemical properties of cis trans isomers
Structural isomers have very different physical and chemical properties. The more different the molecule, the more different the properties.
Enantiometers
A chiral carbon atom (when the atom is assymetrical, nonsuperimposable mirror images of each other)
Optical activity in enantiometers
Two enantiometers formed by a chiral carbon atom can rotate light by the same amount but in opposite directions.
Polarimeter
Detects and measures optical activity of enantiometers
Racemic mixture
If both enantiometers are present in equal amounts, the two rotations are cancelled out and the mixture becomes optically inactive called racemic.
Physical properties of enantiomers
Ability to rotate a place of light by the same amount but in opposite directions. Physical properties are identical.
Chemical properties of enantiomers
Identical except when they interact with other optically active compounds
How to seperate a racemic mixture?
Use a chiral column chromatography.
Diastereomerism
When a molecule contains two or more chiral carbon atoms. Several stereoisomers are possible. Known as enantiomers when mirror images and diastereomers when not mirror images. 2+ stereoisomers have different configurations at the stereocentres
How does the electromagnetic spectrum help in spectroscopy?
Depending on the amount of energy involved, different types of transitions occur in different regions of the electromagnetic spectrum.
When can mass spectroscopy be used?
At low pressures and high voltages when the compound can break down into seperate fragments.
How does infrared spectroscopy work?
When bonds bend/stretch, they vibrate and this causes a change in the dipole moment of the molecule, so it absorbs energy in the IR region. The frequency of the energy depends on the bond.
Why do greenhouse gases absorb infrared energy?
Molecules vibrate as bonds move. Energy associated with the bond vibrations is infrared energy. If there is a change in dipole, vibrations are IR active.
Greenhouse gases (3)
CH4, CO2, H2O
H20 vibrational modes
All infrared active (symmetrical stretch, asymmetrical stretch, symmetrical bend)
CO2 vibrational modes
Symmetrical stretch is IR inactive, asymmetrical stretching and symmetrical bending are IR active
First alkane that contains more than one symbol in H1NMR
Propane
The area under a signal depends on -
The number of nuclei in that chemical environment
Why don’t protons bonded to the same atom interact?
They are equivalent and behave as a group
Why do protons on adjacent carbon atoms not interact?
They are too far apart for magnetic fields to interact through spin spin coupling
Signal for OH protons
Is not split by other protons and appears as singlets
