IR plastics Flashcards
Why does C-O have a higher wavenumber than C-Cl?
C-Cl has a larger mass, and mass is inversely proportional to wavenumber. Therefore the large mass = low wavenumber
Why does C=O have a larger wavenumber than C-O?
Higher bond order means higher energy, energy is proportional to wavenumber
Wavenumber is proportional to
Energy, frequency, dipole moment
Wavenumber is inversely proportional to
wavelength and mass
All materials are
different in their atomic, molecular, and bonding compositions
What are polymers
macromolecules (large molecules) made up of monomers
what are monomers?
repeating units
what does n mean?
the number of monomers in a polymer
PETE
Polyethylene Terephthalate
HDPE
High Density Polyethylene
PVC/V
Polyvinyl chloride
LDPE
Low Density Polyethylene
PP
Polypropylene
PS
Polystyrene
Types of molecular vibrations
Stretches and bends
Types of stretches
Asymmetric and Symmetric
Types of bends
In or out of plane and scissor
Mixture of different polymers
Polymer blend
X-Ray Photoelectron Spectroscopy (XPS)
identifies the surface chemistry of different plastics including colour and width.
ie. a black plastic would be indecipherable in IR
Infrared Spectroscopy (IR)
identifies the functional groups of polymers, meaning it can differentiate between plastics of the same family (Polyethylene)
If a peak is found at a higher wavenumber what does that mean?
that it represents a higher energy dipole bond
What does the wavenumber of absorbed light depend on?
the atom’s bonding environment (dipoles, bond order, vibration, type of atoms etc)
IR light detects what?
wavelengths that are absorbed and or transmitted
Region left of the peak
the functional group region, useful to analyzing specific bonds in unknown structures
Region right of the peak
the fingerprint region, unique to every molecule
sp², C-H stretch
3000-3100
sp³, C-H stretch
2840-3000
CH3 Bend
1350-1475
CH2 bend
1450-1475
C=O stretch
1650-1770
C=C ring pair stretch
1400-1500 and 1585-1600
C-O stretch
1200-1310
C-Cl stretch
550-850
O-H stretch
3000 - 3300
usually very broad and weak
Type of IR used during this experiment
ATR-IR
How do you calculate the amount of light absorbed
measuring intensity of light entering crystal and intensity of light reaching the detector
Why does a sp³ occur at lower wavenumbers than sp²?
The double bond of the sigma framework of sp2 requires more energy to break/vibrate bc it has more s character which leads to shorter and stronger bonds.
Why does the acetate ion only have a peak at 1400?
Because of the C-H bend that is there (sp^3), because the acetate ion looses the H ion that allows it to vibrate so it vibrates less and the C-O bond is completely eliminated
Can IR distinguish well between LDPE and HDPE?
To a certain extent bc one certain peak, but there are other ways that do it better
differential scanning calorimetry (DCS) works better because they use physical properties
Difference between LDPE and HDPE
LDPE has an “R” group, limiting its bonds with other monomers, leading to a linear structure that is flexible
HDPE is a long branching chain of monomers that can pack together, making it firmer and rigid.
