Flashcards in L5 Rich: uv-visible spectroscopy Deck (66):
when reds absorbed what's wavelength and transmitted colour?
when orange absorbed what's wavelength and transmitted colour?
when yellow absorbed what's wavelength and transmitted colour?
when greens absorbed what's wavelength and transmitted colour?
when blue absorbed what's wavelength and transmitted colour?
when violet absorbed what's wavelength and transmitted colour?
what part can the human see?
the UV Vis region
does UV vis tell us about the structure of a molecule?
what does Uv vis tell us about?
quantity, absorption maximum.
what does a commercial spectrophotometer over?
185 –900 nm range
with a commercial spectrophotometer where can you get interference?
190, as water and oxygen in the air will cause peaks
what is the origin absorption of Electronic Spectroscopy of Molecules?
Interaction of photons with ions or molecules
what happens when a molecule absorbs a photon ?
when a molecule absorbs a photon form the Uv visible region, the energy is captured by the outer most electrons and leads to a change in electronic energy
Does UV vis cause a change in vibrational energy?
no that happens in Raman spectroscopy
what does the change in electronic energy levels cause?
Results in alteration of vibrational and rotational energy
how many wave numbers do we need for UV vis spectroscopy ?
10,000 wave numbers in energy
when carrying out Uv vis spectroscopy what peaks do we see?
mainly broad peaks
(covers multiple peaks occurring ta the same time)
absorption of photons takes how long?
in uv vis what stem axis of the graph
what stem units of wavelength?
what is transmittance?
measure of intensities of transmitted and incident light
in ramane and infrared the x axis is in?
what's transmittance equation?
what happens when UV vis is does on gases?
spectra shows fine structure, vibrational transitions - big peaks
rotational transitions - within big peaks
For Uv vis whats the sample prep?
- dissolve sample into solution
what can uV vis be done on?
gas liquid and solid
water has a maximum absorption wavelength of?
190nm ( in UV)
polar solid will need a ?
when preparing for Uv vis you need to know?
cuvettes come in?
Quartz or glass or plastic
is glass cuvettes used during UV?
no use quartz
when using organic solvents, don't use?
what's the beer lambert law equation?
what is A?
molar absorption coefficient
dm3 mol-1 cm-1
concentration in mol dm-3
path length in cm (usually 1 )
what do you plot?
C against A (straight diagonal line)
whats the other equation?
A= - log 10T
Uv vis spectroscopy mainly uses ?
How many transmissions do we need to know?
what are the 2 transmissions?
n electron to lowest π* anti bonding orbital
when does n →π* happen?
heteroatom with lone pair of electrons
highest π orbital to lowest π* anti bonding orbital.
which has a more intense peak?
which has a small peak?
in transition metal compounds what transition happens?
d → d
for d → d what do you need?
partially filled d orbitals
what colour is chlorophyll?
what are chromophore groups functional for?
Functional groups responsible for absorption
what happens to the band of a chromophore group ?
Position and intensity of absorption band constant for
what is conjugation?
when the π character spreads out over carbon chain
what do conjugated systems do?
change energy between highest π MO and lowest π* MO
more conjugated bonds means?
less energy needed for transition.
if energy for transition is lower than?
wavelength increases (red shift)
more conjugated the system the...
smaller the gap between π and π* , leading to larger wavelegnth
white powders only absorb in the?
UV region not coloured
molecules with N--N?
shot absorption into visible section by reducing pie to pie star gap.
what are molecules with N--N called?
Azo compound are used as?
what are Sudan dyes?
used as food colouring
UV-Visible spectroscopy can be used with?
- Presumptive tests
is Uv vis destructive?
is the new major technique