rientation of Nuclear Spins in an Applied Magnetic Field 수소핵에외부자기장을걸어주면수소핵은전하를띠므로핵자기모멘트가유도 됨 Figure 13.1 : Spin states of 1 and 13 nuclei in t

Size: px

Start display at page:

Download "rientation of Nuclear Spins in an Applied Magnetic Field 수소핵에외부자기장을걸어주면수소핵은전하를띠므로핵자기모멘트가유도 됨 Figure 13.1 : Spin states of 1 and 13 nuclei in t"

인걱 채
6 years ago
Views:

1 47 hap 13 Nuclear Magnetic Resonance Spectroscopy 13.1 Nuclear spin states 13.2 rientation of nuclear spins in an applied magnetic field 13.3 Nuclear magnetic resonance 13.4 An NMR spectrometer 13.5 Equivalent hydrogens 13.6 Spin areas 13.7 hemical shift 13.8 Signal splitting and the (n+1) rule 13.9 The origins of signal splitting NMR Interpretation of NMR spectra Nuclear Magnetic Resonance(NMR) Spectroscopy( 핵자기공명분광법 ) : 원자에 자기장을걸어줄때핵이 spin 하는현상을이용하여원자의환경을분석하는방법 1 NMR - 수소에관한정보 13 NMR - 탄소에관한정보 13.1 Nuclear Spin States ( 핵스핀상태 ) Atomic nuclei - 원자번호혹은질량이홀수값은가질때 spin 성질을가짐 Spin state의개수 : (2I +1) allowed spin states I = nuclear spin quantum number ( 핵스핀양자수 ) 2I +1 = -I, -I+1,, +I-1, +I e.g. 1, I=1/2 2 D, I=1 2I+1 = -1/2, +1/2 (2 states) 2I+1 = -1, 0, +1 (3 states) Table 13.1 : Spin quantum number and nuclear spin state of elements

2 rientation of Nuclear Spins in an Applied Magnetic Field 수소핵에외부자기장을걸어주면수소핵은전하를띠므로핵자기모멘트가유도 됨 Figure 13.1 : Spin states of 1 and 13 nuclei in the presence of applied magnetic field -1/2 hv +1/2 No field Applied field E = E -1/2 - E +1/2 = h = f(ϒㆍb o ) ϒ : magetogyric ratio( 자기회전비 율 ) = ϒㆍh/2πㆍB o = 핵자기모멘트 / 핵의각운동량 = ϒ/2πㆍB o B o : 외부자기장의세기 B o = Gauss, = 60 Mz E = 2.39 x 10-5 kj/mole = Gauss, = 300 Mz E = 5 x 2.39 x 10-5 kj/mole 핵 spin 들사이의에너지차이는외부자기장의세기에비례하여증가함 Figure 13.2 : Energy difference between allowed nuclear spin states 13.3 Nuclear Magnetic "Resonance" 수소의핵에 Gauss( = 60 Mz) 의자기장을걸어주면수소핵은자신의회전축을중심으로세차운동을한다. 세차운동하는진동수와같은진동수의전자파를쪼여주면이두진동수가짝지어져수소핵의 spin이 +1/2에서 -1/2로바뀌게는현상을 resonance( 공명 ) 이라한다. NMR 기기는이러한 absorption 과정을 signal( 신호 ) 로기록하여수소의환경을분석하게된다. 수소핵의진동수는치환되어있는수소의환경에따라약간씩차이를나타내므로, 공명을일으키는 absorption energy의크기는각각약간씩다르게된다. 즉, 수소가느끼는 순수자기장효과 = 외부자기장세기 - 내부유도자기장세기 이며, 내부유도자기장세기는수소핵주위의 electron density에비례한다. 따라서수소핵주위의전자밀도가클수록순수자기장효과는감소하며, 수소핵주위의전자밀도가작을수록순수자기장효과는증가하여, 결과적으로전자밀도가다른수소를구분할수있게된다.

3 49 Shielding( 가리움 ) B 1 수소핵주위의 electron density 가크면내부유도자기장의세기 (B 1 ) 가커지며, 수소핵이느끼는순수자기장효과 (B o -B 1 ) 는상대적으로작아진다. 순수한외부자기장세기를작게느끼는수소를 shielding 되었다고한다. B o Deshielding( 벗겨짐 ) l l l B 2 수소핵주위의 electron density 가작으면내부유도자기장의세기 (B 2 ) 가작아지며, 수소핵이느끼는순수자기장효과 (B o -B 2 ) 는상대적으로커진다. 순수한외부자기장세기를크게느끼는수소를 deshielding 되었다고한다. B o hemical shift ( 화학적이동, δ) 수소핵의 absorption energy 차이를 shielded compound인 tetramethylsilane (TMS), ( ) 4 Si=0으로정하여상대적인수값으로표기한크기 Shift in z to ( δ = 3 ) 4 Si 단위 : ppm Spectrometer frequency in Mz e.g. hemical shift 360 z 300 x 10 6 z 1.2 = = 1.2 ppm An NMR Spectrometer Figure 13.4 : Schematic diagram of NMR spectrometer NMR 측정 Sample rotation with 40 rpm frequency sweeping Resonance detector recorder Spectrum Sample cell : sample (5~50 mg) + 용매 (l 4, Dl 3, 6 D 6, D 2, D 3 D 3 ) Fourier Transform(FT) NMR : 미량 (1~2 mg) 의 sample 측정, high sensitivity

4 50 Figure 13.5 : 1 NMR spectrum of methyl acetate 수소의화학적이동 Downfield( 낮은장 ) Deshielding δ 증가 Upfield ( 높은장 ) Shielding δ 감소 TMS Equivalent ydrogens hemically equivalent( 화학적동등 ) : 화학적환경이같은수소. 즉, 수소핵주위의 electron density( 전자밀도 ) 가같은수소끼리를화학적으로동등하다라고한다. 화학적으로동등한수소는순수외부자기장효과를똑같이받으므로 chemical shift(δ) 가같다. 2 l 2-Methylbutane Acetone yclopentane (Z)-1-hloropropene yclohexene 문제 13.3 : ne signal of 1 NMR spectrum (c) 5 12 (d) 4 6 l 4

5 Signal Areas Absorption peak 의면적비율 = 수소의상대적인비율 l Methyl-1-chloropropane yclohexene Dimethyl carbonate Figure 13.7 : 1 NMR spectrum of tert-butyl acetate 13.7 hemical Shift hemical shift(δ) - 흡수가일어나는수소의종류에관한정보제공즉, δ의크기로부터수소가어떤작용기에결합되어있는지를대략적으로알수있다. Figure 13.8 : Average values of chemical shifts of various protons 예제 13.5 : 분자식 인 2 개의구조이성질체 (a) no of signals (b) ratio of area (c) identification of isomer by δ tert-butyl acetate Methyl 2,2-dimethylpropanoate A. Electronegativity of Nearby Atoms -X에서 X의전기음성도가클수록수소핵주위의전자밀도는감소하게되므로 deshielding이일어나 chemical shift의크기는증가한다. 이러한전기음성도효과는거리가멀어질수록급격하게감소한다. Table 13.2 : Dependence of chemical shift of X on the electronegativity of X

6 52 B. ybridization of Adjacent Atoms 혼성탄소의 s 성질이증가할수록전자를잘흡인하므로수소핵주위의전자밀도가감소하여 deshielding이일어나 chemical shift의크기는증가한다. Table 13.3 : The effect of hybridization on chemical shift. Diamagnetic Effects( 반자기성효과 ) from π Bonds - (sp 3 ) δ 0.8~1.7 =- (sp 2 ) δ 4.6~5.7 - (sp) δ 2.0~ (sp 2 ) δ 6.5~8.5 Figure 13.9 : Magnetic field induced in pi(π) bond of in acetylene Figure : Magnetic field induced in pi(π) bond of = in benzene

12.2 Molecular Spectroscopy ( 분자분광학 ) 분자에전자기복사선을쪼여주면분자가낮은에너지상태에서높은에너지상태로이동하게되며, 이때특정흡수진동수를이용하여분자의구조를알아낼수있다. Figure 12.1 : Absorption of energy in elec

12.2 Molecular Spectroscopy ( 분자분광학 ) 분자에전자기복사선을쪼여주면분자가낮은에너지상태에서높은에너지상태로이동하게되며, 이때특정흡수진동수를이용하여분자의구조를알아낼수있다. Figure 12.1 : Absorption of energy in elec 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