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The questions are on the page that says "IR/GC-MS part 2". Answer those questions based off the spectra
IR Spectroscopy and GC/MS Part 2 In trying to analyze the spectrum of an unknown, you should concentrate your first efforts toward determining the presence or absence of a few major functional grov R Below is a check list of the major functional groups you should be able to identify by IR spectroscopy. 1. Is a carbonyl group present? Look for a strong absorption in the region 1820-1660 cm-1. The peak is usually the strongest peak in the spectrum (you can't miss it). If it is present, you should try to determine the functional group. Use the correlation table. Also, consider the following. a. A carboxylic acid should also have an O-H present (broad band 3200-2500 cm²¹) b. An amide should also have an N-H present (sharp band 3400-3250 cm³¹) c. An acid anhydride should have 2 C-O peaks. d. An ester should also have a C-O (strong band 1300-1000 cm) e. An aldehyde should have 2 C-H peaks (weak 2850-2750 cm¹¹ ) f. A ketone by process of elimination 2. If there is no carbonyl, is there an O-H? Look for a broad O-H band in the region 3500-3200 cm¹. If there is such a band, it indicates an alcohol or phenol. 3. Is there an N-H? Look for a single or double sharp N-H band in the region 3400- 3250 cm. If there is, two bands indicates a primary amine, one band indicates a secondary amine. 4. Is there a C-C? Aromatic rings and alkenes indicated by peaks (1650-1450 cm³¹) 5. Is there a triple bond? Nitriles and alkynes give peaks (2260-2100 cm³¹) 6. Is there a NO₂ group? Two strong absorptions (1550- 1475 cm & 1360-1290 cm'¹) 7. If there is an absence of major functional group bands in the region 4000-1300 cm™¹ (other than C-H stretches), the compound is probably a strict hydrocarbon. The beginning student should resist the idea of interpreting every peak in the spectrum. Get the major functional groups and suggest a structure which is consistent with the data. It is often impossible to generate a unique structure based on the IR alone; it is possible to narrow down the possible structures. Generally IR is used in conjunction with other types of analysis, such as NMR, to determine the exact structure of the compound. If you are provided with a molecular formula, calculate the degree of unsaturation to limit the number of possible structures. The degree of unsaturation indicates whether or not the compound has one or more n bonds and/or rings. You can use this information to limit the number of structures to consider.
From the formula shown, you can calculate the degree of unsaturation, which is the number of r bonds and/or rings present in the molecule: degree of unsaturation (DOU)= [(2C+2) -H-X+N] where C = # of carbons, H = # of hydrogens, X = # of halogens, and N = # of nitrogens. When the molecule is acyclic (there are no rings) and there are no C-C double bonds or functional groups like ketones, esters, etc. the degree of unsaturation is zero. Each double bond or ring adds one degree. A triple bond adds two degrees. If the degree of unsaturation is 4 or more, then there is a good chance that the molecule contains an aromatic ring. You will be using the IR spectra obtained in Part I with GC-MS provided by your instructor to propose at least TWO possible structures for each unknown that is consistent with your data. To aid in your derivation, you will need to identify the molecular ion peak (if present), the base peak, any relevant fragments that helped in your determination, a possible molecular formula, units (degrees) of unsaturation, and any functional groups.
4000 3500 3000 2500 Wavenumbers (cm-1) 2000 1500 1000 500 40 845.96 45 50 55 % Transmittance 60 2225.71 1228.53 828.91 75 1503,29 1413.14 1287.74 1021.27 734.88 80 1934.26 1203.37 1179.80 1096.70 3067.90 764.57 1810.65 1690.18 1606.70 1440.08 974.21 962.93 877.83 696.24 85
IR/GC-MS part 2 assignment Unknown ATR Solid: Molecular Ion Peak: Base Peak: Important IR peaks present in your unknown. For each peak identify the following: frequency of peak, bond absorbing, functional group containing that bond. Molecular Formula: Show work below for molecular formula: Degrees of Unsaturation: Show work below for DOU: Proposed Structures (2):