39 hap 12 Infrared Spectroscopy ( 적외선분광학 ) 12.1 Electromagnetic radiation 12.2 Molecular spectroscopy 12.3 Infrared spectroscopy 12.4 Interpreting infrared spectra 12.5 Solving infrared spectral problems 분자의구조결정 : IR에의한작용기의종류파악 1 H NMR에의한수소의종류및상대적인비율을알아내어 alkyl 혹은 aryl기의환경을파악 Mass에의한분자량, 동위원소, 분자의 fragment( 조각 ) 파악 12.1 Electromagnetic Radiation ( 전자기복사선 ) 전자기복사선 : γ- 선, X- 선, Ultraviolet(Uv, 자외선 ), Visible( 가시광선 ), Infrared ( 적외선 ), Microwave, Radio wave Table 12.1 : Wavelength, frequency, and energy of electromagnetic radiation Infrared(IR) : 파장 = 2.5 x 10-6 m ~ 2.5 x 10-5 m Wavelength ( 파장, λ), frequency ( 진동수, ν), energy (E) 의관계식 c = νㆍλ c = 빛의속도 (3 10 8 m/sec = 3 10 10 cm/sec) ν = 진동수 ( 단위, Hz) E = hㆍν = hㆍc/λ = hㆍcㆍν E = 에너지, kj/mol(kcal/mol) ν = 1/λ h = Planck 상수 (3.99x10-13 kjㆍsㆍmol -1 ) ν = wavenumber, cm -1
12.2 Molecular Spectroscopy ( 분자분광학 ) 분자에전자기복사선을쪼여주면분자가낮은에너지상태에서높은에너지상태로이동하게되며, 이때특정흡수진동수를이용하여분자의구조를알아낼수있다. Figure 12.1 : Absorption of energy in electromagnetic radiation Table 12.3 : Types of energy transition resulting from electromagnetic radiation 12.3 Infrared Spectroscopy A. The Vibrational Infrared Spectrum ( 진동적외선스펙트럼 ) 분자에적외선을쪼여줄때작용기가특정한크기의파장을흡수하여 vibration( 진동 ) 하는현상을나타낸스펙트럼 적외선영역 : λ = 2.5 x 10-6 m ~ 2.5 x 10-5 m 10-2 m cm -1 ㆍ ν = ν = 2.5 x 10-6 = 4000 cm -1 10-2 m ㆍcm -1 m 2.5 x 10-5 m = 400 cm -1 μ(μm) x cm -1 = 10,000 e.g. 4 μm cm -1 (ν) ν = λ 1 = 1 4 x 10-6 m 1 = 4 x 10-4 cm = 2.5 x 10 3 cm -1 (4 μm) x (2.5 x 10 3 cm -1 ) = 10000 Figure 12.2 : Infrared spectrum of 3-methyl-2-butanone
41 B. Molecular Vibrations ( 분자진동 ) 분자에적외선을쪼여주면공유결합에의하여결합된원자들은계속적으로진동을일으키며, 이때진동에필요한에너지는양자화되어있으므로특정한에너지준위만허용된다. 분자가적외선을흡수하게되면작용기의쌍극자모멘트가변하게되고, 이를측정하여 recorder로그린것이 IR의 absorption spectrum이다. IR active : l H H 3 IR inactive : H 3 H 3 H H H 3 H 3 H 3 H 3 H 3 Acetone hloroethylene 2,3-Dimethyl-2-butene 2-Butyne 진동운동의형태 : Stretching( 신축 ) vibration 과 bending( 굽힘 ) vibration Figure 12.3 : Stretching and bending vibration of H 2. haracteristic Absorption Patterns 작용기의 stretching vibration 의에너지크기 (ν, cm -1 ) 의예측 : Harmonic oscillator model 에서 Hooke 의법칙활용 ν = 4.12 K μ K = force constant, dyne/cm μ = reduced mass ( 환산질량 ) = m 1 x m 2 m 1 + m 2 m 1, m 2 = 원자량 e.g. -H stretching vibration 의 wavenumber 문제 12.2 : Higher frequency of some functional group
42 D. orrelation Tables Bond ompound Stretching frequency, cm -1 Intensity -H Alkanes 2850 ~ 3000 medium Alkenes 3000 ~ 3100 weak to medium Aromatics 3000 ~ 3100 weak to medium Alkynes 3300 medium to strong = Alkenes 1600 ~ 1680 (1650) medium to strong Alkynes 2100 ~ 2250 medium RH, RR, = - RH, RR', RNH 2, (R) 2 RR', RR', RH 1630 ~ 1810 strong 1000 ~ 1250 strong -H Alcohols 3200 ~ 3650 strong(broad) N-H Amines 3100 ~ 3500 medium(slightly broad) 예제 12.4 : 구조이성질체의구분
43 12.4 Interpreting Infrared Spectra A. Alkanes, alkenes, alkynes, and arenes Table 12.5 Infrared absorptions of alkanes, alkenes, alkynes, and arenes Hydrocarbons Vibration Frequency, cm -1 Intensity Alkanes -H Stretching 2850 ~ 3000 medium H 2 Bending 1450 ~ 1475 medium H 3 Bending 1375, 1450 weak to medium Alkenes -H Stretching 3000 ~ 3100 weak to medium = Stretching 1600 ~ 1680 (1650) medium to strong Alkynes -H Stretching 3300 medium to strong Stretching 2100 ~ 2250 medium Arenes -H Stretching 3030 weak to medium = Stretching 1450 ~ 1600 medium -H Bending 690 ~ 900 strong Figure 12.4, 12.5, 12.6, 12.7 : Ir spectrum of decane, cyclohexene, 1-octyne, toluene
44 B. Alcohols ν -H (stretching) = 3200 ~ 3650 cm -1 (hydrogen bonded, strong) 3600 ~ 3650 cm -1 (free, weak) ν - (stretching) = 1050 ~ 1250 cm -1 (strong) Figure 12.8 : Ir spectrum of 1-hexanol. Ethers Symmetrical aliphatic ether : ν - (stretching) = 1000~1100 cm -1 (one band) Unsymmetrical aromatic ether : ν - (stretching) = ~1250 cm -1 (asymmetric) ~1050 cm -1 (symmetric) Figure 12.9, 12.10 : Ir spectrum of dibutyl ether, anisole D. Amines ν N-H (stretching) = 3300 ~ 3500 cm -1 (medium, slightly broad) RNH 2-2 bands R 2 NH - 1 band R 3 N - no band Figure 12.11 : Ir spectrum of 1-butanamine (1 o amine) E. Aldehydes and Ketones RH : ν = = 1725 cm -1 (strong) RR : ν = = 1715 cm -1 (strong) ν -H = 2720 cm -1 (weak) Ring size 에대한 = stretching frequency 의변화 1715 cm -1 1745 cm -1 1780 cm -1 1850 cm -1
45 = stretching frequency 에대한 conjugation effect H 1717 cm -1 1690 cm -1 1700 cm -1 Figure 12.12 : Ir spectrum of menthone F. arboxylic Acids and Its Derivatives Table 12.7 : Infrared Absorptions of Molecules ontaining arbonyl Groups arbonyl compounds R R' Bond Frequency, cm -1 Intensity = 1715 = 1710 R H -H 2500 ~ 3300 (very broad) = 1735 R R' - 1000 ~ 1250 = 1760, 1820 (2 bands) R R' - 900 ~ 1300 R N N 2200 ~ 2250 Medium Figure 12.13, 12.14, 12.15 : Ir spectrum of pentanoic acid, N-methylpropanamide, ethyl butanoate
46 Problems 12.7 IR spectrum of 2-methyl-1-butanol and tert-butyl methyl ether 12.10 Functional group (a) 1735, 1250, 1100 cm -1 (c) 1710 and 2500~3400 cm -1 12.11 haracteristic stretching frequency (b) H (d) H 3 (h) (j) H H