ORGANIC - BROWN 8E CH INFRARED SPECTROSCOPY.

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2 CONCEPT: PURPOSE OF ANALYTICAL TECHNIQUES Classical Methods (Wet Chemistry): Chemists needed to run dozens of chemical reactions to determine the type of molecules in a compound. EXAMPLE: Tollen s Test Instrumental Methods (Dry Chemistry): Expensive scientific instruments investigate the properties of molecules. EXAMPLE: 1 H NMR Page 2

3 CONCEPT: IR SPECTROSCOPY- GENERAL FEATURES IR Spectroscopy is a chemical analytical method that uses differing frequencies of infrared light to detect predictable types of chemical bonds in molecules. The frequencies will cause certain bonds to Stretching, Twisting, Wagging, Scissoring, etc. If the molecule is symmetrical, e.g. N2, the band is not observed in the IR spectrum. Major regions of absorption Common IR Ranges OH Strong, Broad NH Peaks = H s SP3 = SP2 = SP = CH C C C N Choppy Medium, Sharp 1700 C=O Very Strong, Sharp 1650 C=C Medium, Sharp Page 3

4 CONCEPT: IR SPECTROSCOPY- FREQUENCIES There are specific absorption frequencies in the functional group region that we should be familiar with EXAMPLE: What are the major IR absorptions for each compounds? Page 4

5 PRACTICE: Answer each of the following questions based on the images below. O OH O O O H F 3 C O CF 3 A B C D E a) Which compounds show an intense peak ~ 1700 cm -1? b) Which compound shows an intense, broad peak at ~ 3400 cm -1? c) Which compound has a peak at ~1700 cm -1, but no peaks at 2700 cm -1? d) Which compound has no signal beyond the fingerprint region? Page 5

6 PRACTICE: The following compound contains two carbonyl groups. Identify which carbonyl group will exhibit a signal at a lower wavenumber. O O Page 6

7 CONCEPT: IR SPECTROSCOPY- DRAWING HYDROCARBONS Alkanes: Alkenes: Terminal Alkynes: Page 7

8 CONCEPT: IR SPECTROSCOPY- DRAWING ALCOHOLS AND AMINES Alcohols: 1 Amines: 2 Amines: Page 8

9 CONCEPT: IR SPECTROSCOPY- DRAWING SIMPLE CARBONYLS Ketones: Esters: Page 9

10 CONCEPT: IR SPECTROSCOPY- DRAWING COMPLEX CARBONYLS Aldehydes: Carboxylic Acids: Page 10

11 CONCEPT: IR SPECTROSCOPY- DRAWING CONCEALED FUNCTIONAL GROUPS Alkyl Haldies: Ethers: 3 Amines: Page 11

12 PRACTICE: Based on IR data given determine the structure of the unknown. Unknown compound A has molecular formula C4H11N. It shows a peak at 2900 cm -1 and peaks in the fingerprint region. PRACTICE: Based on IR data given determine the structure of the unknown. Unknown compound B has molecular formula C4H11N. It shows a single peak at approximately 3400 cm -1 as well as peaks at 2900 cm -1 and in the fingerprint region. Compound B also possesses a branched alkyl group. PRACTICE: Based on IR data given determine the structure of the unknown. Unknown compound C has molecular formula C6H10O3. It shows peaks at 2900, 1850, 1740 cm -1 and in the fingerprint region. Page 12

13 PRACTICE: Match the following functional group choices with the supplied infrared spectra data A) Ether B) Ketone C) Alcohol D) Alkene E) Nitrile Page 13

14 PRACTICE: Match the following functional group choices with the supplied infrared spectra data. A) Alkyl Halide B) Alkyne C) Carboxylic Acid D) Alkene E) Ketone Page 14

15 PRACTICE: Match the following functional group choices with the supplied infrared spectra data. A) Aldehyde B) Alkane C) Carboxylic Acid D) Ester E) Ether PRACTICE: Match the following functional group choices with the supplied infrared spectra data. A) Ketone B) Alkyne C) Alkene D) Alkyl Halide E) Amine Page 15