Chapter 17 - Spectroscopy (MODULE 4) Flashcards
What do mass spectra show
- what can it be used to identify
the mass to charge ratio of ions
- the molecular mass of an organic compound
What happens to an organic compound before it is placed in the mass spectrometer
loses an electron to become a 1+ ion
What is the furthest right peak on a mass spectrometer
M+ peak / molecular ion peak
What is on the x and y axis on a mass spectrometer
x - m/z ratio
y - relative intensity
What do the peaks in a mass spectrometer represent
m/z of fragments of the ion
Why does the M+1 peak exist
Because 1.1% of carbon is present as the C-13 isotope
What is fragmentation
When the molecular ion breaks into smaller fragment ions
What is formed when a molecular ion breaks into 2 fragments
a fragment ion and a radical
Why can mass spectroscopy be used to identify an organic molecule
because each molecule breaks into a different combination of fragments and so each has a unique mass spectra
What are the m/z values for:
CH3+
CH3CH2+
CH3CH2CH2+
COOH+
COH+
- 15
- 29
- 43
- 45
- 29
Why do covalent bonds bend and stretch
bonds have energy and vibrate, causing them to bend or stretch
What is a stretch of a covalent bond
movement along the line between atoms so distance between the two atomic centres increases and decreases
What two things does the stretch or bend of a bond depend on, and what are their effects
mass of atoms - heavier atoms vibrate more slowly than lighter atoms
strength of bond - stronger bonds vibrate faster than weaker bonds
What happens to IR radiation from the sun
passes through to the Earth’s surface, where most is absorbed. Some is reemitted as longer-wavelength IR radiation
Why do gases such as H2O, CO2 and CH4 cause the greenhouse effect
absorbs IR radiation as their bonds vibrate at a similar frequency. This is then re-emitted as radiation increasing the temperature of the atmosphere
What is IR spectroscopy used for
identifying the functional groups present in organic molecules
What are the 4 steps to IR spectroscopy
- sample placed in IR spec
- beam of IR radiation is passed through the sample
- molecule absorbs some IR frequencies and emerging beam is analysed to identify what is absorbed
- computer plots graph of transmittance against wavenumber
What do peaks in the IR spec show
the wavenumber of bonds present in the compound
What is the region below 1500 /cm on an IR spec called
fingerprint region
What is the wavenumber of:
C=C
C=O
C-H
O-H (carboxylic acid)
O-H (alcohol)
1620 - 1680 /cm
1630 - 1820 /cm
2850 - 3100 /cm
broad - 2500 - 3300 /cm
3200 - 3600 /cm
Where is the characteristic peak on an alcohol (wavenumber)
3200 - 3600
Where is the characteristic peak on a ketone (wavenumber)
around 1700
Where are the characteristic peaks of a carboxylic acid (wavenumber)
1630 - 1820 & broad 2500 - 3300
How can IR spectroscopy be used in roadside alcohol tests
scans for O-H group in breath
