3.6 - Organic Analysis Flashcards
What does the Position of each Inverted Peak/Absorption show?
Which bonds are present & ∴ which functional groups are present in organic compound
What are Fragment ions?
Ions caused by Break up of unstable Molecular ion
What is the Fingerprint Region?
Region below 1500cm⁻¹ which is unique to a compound
Computer compared this to database ∴ identifying the compound
What is an I-R spectrum?
A graph of % transmittance against wave number (cm⁻¹)
What is Wavenumber proportional to?
Frequency
What can the results of the Combustion of organic substances be used to determine?
Empirical Formula of Compound
What is Infra-red Spectroscopy?
Analytical technique used to Identify types of Organic compounds
Why is there sometimes a Small Peak above Molecular ion Peak?
Presence of Carbon-13 Isotope
When is High res mass spectrometry useful?
When compounds have the same whole no. Mr
e.g. propan-1-ol & ethanoic acid
Three main Greenhouse gases?
CO₂
CH₄
H₂O
Easy to Identify Characteristic of O-H peaks?
Smooth Peak
Test for Aldehydes?
Tollens’ - Silver Mirror
Acidified Potassium Dichromate - Orange |> Green
Fehling’s - Blue Solution |> Brick Red ppt.
How do you calculate Empirical Formula?
Mass
Ar
moles
Simplest Ratio
Between CO₂ & H₂O, which absorbs & re-emits more
I-R radiation?
H₂O as O-H peak has larger absorption area
Test for Carboxylic Acids?
Na₂CO₃ - fizz (CO₂)
Universal indicator - red/orange
Test for Alkenes?
Decolourises Bromine Water
How many decimal places can a High-res Mass Spectrometer measure Ar & Mr to?
4
When are Fingerprint regions most Useful?
When the same bonds are present in the compounds analysed
Why do CO₂, CH₄ & H₂O absorb infrared radiation?
Contain C=O
O-H or
C-H bonds
Test for Primary & Secondary Alcohols?
Acidified Potassium Dichromate
H⁺/Cr₂O₇²⁻
Orange |> Green
Define: Molecular ion Peak
Line w/ largest m/z (mass to charge) ratio, giving Mr of compound
Test for Tertiary Alcohols?
Acidified Potassium Dichromate
H⁺/Cr₂O₇²⁻
No Visible change
What are the lines on a Mass Spectrum due to?
Fragment ions
&
Molecular ion
What is Infra-red Spectroscopy used for?
|> To detect presence of specific covalent bonds in a compound
|> Each type of bond vibrates at specific frequency & so absorbs specific frequency of I-R radiation
How do you calculate Empirical Formula from masses of CO₂ & H₂O after combustion of CxHyOz in excess oxygen?
|> Calculate moles of CO₂ & H₂O
|> Calculate moles of C (same as CO₂)
|> Calculate moles of H (moles of H₂O x 2)
|> Calculate mass of C (x12)
|> Calculate mass of H (x1)
|> Calculate mass of O
|> Calculate Empirical Formula from: masses, Ar, moles, then Simplest Ratio
Test for Halogenoalkanes?
AgNO₃
Cl⁻ - white ppt
Br⁻ - cream ppt
I⁻ - yellow ppt
Alcohols react with Sodium to form ____ ?
Salt & Hydrogen
