Solution Manual For Spectrometric Identification of Organic Compounds, 8th Edition

CHAPTER 2 2.1 1 ?1?2 ? = 2?c √? (?1+?2) (k) force constant = 42c2 v2 meff ?1?2 meff = (?1+?2) (1.0078 x 18.9984) meff = (1H19F) = (1.0078 + 18.9984) = 0.9570 µ meff = (1H35Cl) =0.9796 µ meff = (1H81Br) =0.9954 µ meff = (1H127I)=0.9999 µ (k) (1H19F) = 4 x 3.142 x (2.997 x 1010 cm s-1)2 x (4148.2 cm-1)2 x (0.9570 x 1.66 x 10-27kg) =968.3 kg s-2 =968.3 N/m (k) (1H35Cl) = 514.6 N/m (k) (1H81Br) = 410.9 N/m (k) (1H127I) = 313.6 N/m Assume that the force constant for halides are the same when substituting the deuterium — the calculated bond stretch frequency for halides: 1 ?1?2 ? = 2?c √? (?1+?2) 2.2. The gross selection rule for infrared activity is that motion corresponding to a normal mode should be accompanied by a change of dipole moment. So those molecules in which a vibration gives rise to a change in dipole moment are infrared active compounds: (a) CH3CH3, (b) CH4, (c) CH3Cl. It is helpful to write down the structural formulas of the compounds 2.3. A nonlinear molecule has 3N-6 normal modes of vibration, where N is the number of atoms in the molecule; a linear molecule has 3N-5. (a) C6H6 has 3(12) – 6 = 30 normal modes (b) C6H6CH3 has 3(16) – 6 = 42 normal modes (c) HC≡C-C≡CH is linear; it has 3(6) – 5 = 13 normal modes 2.4. From top to bottom the: o-xylene, m-xylene, then p-xylene CHAPTER 2 2.5. 2.6. For butyric acid and ethyl butyrate, the carbonyl stretching band is a result of a simple fundamental stretching mode. Butyric anhydride, on the other hand, exhibits 2 carbonyl stretching frequencies due to coupling of the carbonyls through the common oxygen atom of the anhydride functional group. The 2 frequencies are respectively the symmetric and asymmetric stretching frequencies. 2.7. Combination bands are a result of complex interactions between 2 or more fundamental vibration modes. For instance, if a fundamental vibration does not occur because of the wrong symmetry, it can combine with another fundamental frequency of proper symmetry to produce one or more combination band. A series of useful combination bands is often found between 1700 and 2000 cm-1 for aromatic compounds. For an oscillator, the lowest “natural” frequency is called the fundamental frequency (n=1). Higher order frequencies are called “overtones”. The first overtone (n=2) can be found at approximately twice the frequency of the fundamental frequency. Higher overtones are possible but rarely seen. A common overtone band found in IR spectra is the first overtone band of the carbonyl stretch of ketones. The fundamental frequency is typically found at 1715 cm -1 while the first overtone is often seen at approximately 3420 cm-1. 2.8. Table 2.10 is used to determine this answer. The more electronegative the functional groups are, the higher the P-O IR stretching frequency. OCH3 O P OCH3 F O P CH3 O CH3 OCH3 O P OCH3 CH3 O P OCH3 OCH3 CH3 OCH3 3 7 1 5 OC6H5 OCH2CH3 P OCH3 O P OCH2CH3 OCH3 OCH2CH3 6 4 CH3 O P OCH2CH3 OCH2CH3 2 CHAPTER 2 2.9 OH O Br Br 4-Heptanone 3-Heptanol 4-Bromotoluene 2-Bromopentane A B C D O O OH H 2N OH 2-Hexanone Propionic Acid Butylamine Propargyl alcohol E F G H O N+ OH O- O O O O 1-Nitropropane 2-Phenoxylethanol Phenetole MethylHButyrate I J K L HO O O N HN O N+ N O – Cl O Caprolactam 2-methylpyrazine Methyl salicylate 1-Chloro-4-Nitrobenzene M N O P O O HO Br HO 7-Bromo Heptanoic Acid 5-Hexyn-1-ol 6-Methyl-5-hepten-2-one Q R S HO Cl O HO O Cl HO Hexanoic acid T 2,6-Dichlorophenol U 2,6-Dimethylphenol 2-Cyclohexen-1-one V W