Summary
Summary Module 4.2.4 Chapter 17 Spectroscopy
- Course
- Institution
notes on: 1 - mass spectrometry 2 - infrared spectroscopy
[Show more]
Seller
Follow
saimabegum
Content preview
17.1 mass spectrometryMolecular and - In spectrometer – compound loses e- -> +ve ion = molecular ion (M+)
fragment ions - Mass spectrometer – detects mass: charge of ion – gives molecular mass of compound.
Molecular mass - To find mass – M+ peak (furthest on x axis) = molecular mass.
- M+1 peak – small peak after M+ - 1.1% of carbon is present as C13 isotope.
fragmentation - Some molecular ions break down into fragments – other peaks are caused by fragment ions.
- Fragment ions – formed from breakdown of the molecular ion.
- Fragmentation – breaks ion into 2 species – radical and +ve fragment.
- +ve is detected by spectrometer but radicals aren't.
Fragmentation - Find the M+ and the M+1 peaks.
peaks – organic - Break the molecule you're looking for up.
molecule - Using peaks on spectrum + molecular mass of fragments – find fragments.
M+ peak - Used to identify number of C atoms present in the compound.
- C = (height of M+1/height of M+) x 100
- Using ruler to measure in mm.
17.2 infrared spectroscopy
Infrared radiation - Bonds have energy and vibrate – as temperature increases, vibration does too.
and covalent bonds - Bonds absorb IR radiation – bend/stretch more (usually 200cm-1 to 4000cm-1)
- Stretch – along the line between the atoms so the distance between 2 centres changes.
- Bend – change in bond angle = mass and strength
- Mass – heavier = slower, lighter = faster
- Stronger = faster, weak = slower.
- Any bond can absorb radiation that has same frequency as natural frequency of bond.
- Frequency too large – wavenumber is used = proportional to frequency.
Infrared and - Sun and IR are unaffected by atmospheric gases – passes through atmosphere to Earth.
atmospheric gases - Some is re-emitted from Earth’s surface in longer-wavelength IR radiation.
- Greenhouse gases absorb the longer wavelength as it has same natural frequency – vibrating
bonds in molecules re-emit energy as radiation – increases temperature of atmosphere -
global warming. - water vapour, CO2 and methane.
Infrared and organic - Infrared spectroscopy – identifying functional groups.
molecules 1) sample placed inside IR spectrometer.
2) beam of IR radiation is passed through sample.
3) molecule absorbs IR frequency and emerging beam of radiation is analysed to find frequencies.
4) IR spectrometer connected to computer – plots graph of transmittance x wavenumber.
- Peaks – dips in graph = observes at wavenumber related to bond in molecule.
- Fingerprint region – area of smaller peaks after a certain point = find molecule using spectra.
Infrared spectra of - From outside region – peaks are clear – using wavenumber from data book.
functional groups - C-H bonds = 2850-3100cm-1
Alcohol - Has absorbance peak of 3200-3600cm-1 = OH bond + Also has 1000-1300cm-1 by CO bond.
Aldehyde or ketone - Has 1630-1820cm-1 = C=O but typically 1700cm-1
Carboxylic acid – 1630 – 1820cm-1 (C=0), 2500-3330cm-1 (OH)
applications - Pollutants can be identified by IR fingerprints – remote sensors - analyse vehicle emissions to
measure + detect carbon monoxide + carbon dioxide and hydrocarbons.
- Breathalysers – pass beam of IR through breath and detect IR absorbance – find ethanol =
more IR = higher reading = more ethanol in breath.
identification Elemental analysis – percentage composition data to determine empirical formula.
Mass spectrometry – molecular ion peak from spectrum to find MR – fragment ions for sections.
Infrared – absorption peaks from spectrum to find bonds and functional groups.
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller saimabegum. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $7.09. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
53068 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now