Beginning our final portfolio work Carry out experiments on known organic functional groups to gain an understanding of what constitutes a positive result. Explain the principle of the tests for a range of aliphatic functional groups (4.1) Carry out a further experiment with unknown organic compounds to Identify a series of colourless organic liquids Explain the absorbance of infra-red radiation in terms of covalent bond vibrations (5.1) Interpret Infra-red and NMR spectra (5.2) of the organic compounds you investigated, annotating major absorbances/peaks that enable you to classify the compounds.

Spectroscopy Spectroscopy is the study of the interaction between matter and electromagnetic radiation. 

Electromagnetic waves are waves that contain an  electric field and a magnetic field and carry energy. They travel at the speed of light.

Electromagnetic spectrum Our spectrophotometers cover approx 300 – 800 nanometers so they just cover the beginning of uv and ir wavelengths RSC animation shows what energies are picked up at different wavelengths

Spectroscopy visited We have already used spectroscopy in our experiments and used a machine called Spectrophotometer. In chemistry, spectrophotometry is the quantitative measurement of the reflection or transmission properties of a material at different wavelengths. spectrophotometry deals with visible light, near-ultraviolet, and near-infrared.

The UV – Visible spectroscopy Routinely used for analysing coloured and colourless liquids in the UV and visible regions of the electromagnetic spectrum. QUALITATIVE analysis QUANTITATIVE analysis Identify an UNKNOWN COMPOUND above 1500 cm-1 functional groups Below 1500 cm-1 fingerprint region You have used the spectrophotometer to Quantitatively analyse the concentration of copper sulphate and Qualitatively to look at the absorption spectrum of chlorophyll. CONCENTRATION of a solution PHOTOSPECTROMETER INFRARED SPECTROMETER

Infrared spectroscopy is qualitatively used to identify organic compounds IR spectroscopy provides a 100% identification if the spectrum is matched. If not, IR at least provides information about the types of bonds present.

Infrared Spectroscopy Infrared Group Analysis Generally, the four primary regions of the IR spectrum Bonds to H O-H single bond N-H single bond C-H single bond Triple bonds C≡C C≡N Double bonds C=O C=N C=C Single Bonds C-C C-N C-O Fingerprint Region 4000 cm-1 2700 cm-1 2000 cm-1 1600 cm-1 400 cm-1

Infrared Spectroscopy Specific groups Alkanes – combination of C-C and C-H bonds Show various C-C stretches and bends between 1360-1470 cm-1 (m) Show C-H between 2800-3000 cm-1 (s) cm -1

n-pentane 2850-2960 cm-1 CH3CH2CH2CH2CH3 sat’d C-H 3000 cm-1 alkane 1470 &1375 cm-1 CH3CH2CH2CH2CH3

Infrared Spectroscopy Specific groups Alkenes – C=C stretch occurs at 1620-1680 cm-1 vinyl C-H stretch occurs at 3000-3100 cm-1 Note that the bonds of alkane are still present! The difference between alkane and alkene C-H is important! If the band is slightly above 3000 it is vinyl C-H or below if its alkane C-H bonds

1-decene 3020-3080 cm-1 C=C 1640-1680 unsat’d C-H 910-920 & 990-1000 RCH=CH2 C=C 1640-1680 alkene

Infrared Spectroscopy Specific groups Alcohols Show a strong, broad band for the O-H stretch from 3200-3400 cm-1 (s, br) this is one of the most recognizable IR bands a band for C-O stretch between 1050-1260 cm-1 (s) The shape is due to the presence of hydrogen bonding 1-butanol

1-butanol 3200-3640 (b) O-H Primary alcohol C-O 1o CH3CH2CH2CH2-OH

Cyclohexyl carboxaldehyde Infrared Spectroscopy Specific groups Aldehydes Show the C=O (carbonyl) stretch from 1720-1740 cm-1(s) Also displays a highly unique C-H stretch as a doublet, 2720 & 2820 cm-1 (w) called a “Fermi doublet” Cyclohexyl carboxaldehyde

Infrared Spectroscopy Specific groups Ketones Simplest of the carbonyl compounds as far as IR spectrum – carbonyl only C=O stretch occurs at 1705-1725 cm-1 (s) 3-methyl-2-pentanone

ketone What is the compound? Aldehyde or ketone ketone

Infrared Spectroscopy Specific groups Carboxylic Acids: Gives the messiest of IR spectra C=O band occurs between 1700-1725 cm-1 The O-H bond has a broad band from 2400-3500 cm-1 (m, br) covering up to half the IR spectrum in some cases 4-phenylbutyric acid

Ethanoic acid

Infrared Spectroscopy Specific groups Amines - Primary Shows the –N-H stretch for NH2 as a doublet between 3200-3500 cm-1 (s-m); -NH2 group shows a deformation band from 1590-1650 cm-1 (w) 2-aminopentane

ethylamine

Infrared Spectroscopy Specific groups Amides C=O stretch occurs from 1640-1680 cm-1 If the amide is primary (-NH2) the N-H stretch occurs from 3200-3500 cm-1 as a doublet I pivalamide

methanamide