P 3 spektrometri proton nmr
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SPEKTROMETRI PROTON NMR
OLEH :YUSBARINA, M.Si
JURUSAN P. KIMIA FTK UIN SUSKA RIAU
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NMR ?
NUCLEAR MAGNETIC RESONANCEATAU
RESONANSI MAGNET INTI
H-NMR C-NMR
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Kegunaan H-NMR?
Memberikan gambaran mengenai :1. Jenis hidrogen2. Jumlah hidrogen3. Lingkungan hidrogen dalam
suatu senyawa
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Prinsip dasar H-NMR?
NMR didasarkan pada penyerapan gelombang radio oleh inti – inti tertentu dalam molekul organik, apabila molekul tersebut berada dalam medan magnet yang kuat
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Fenomena Resonansi Magnetik IntiModel fisika klasik:Inti atom bermuatan positif dan berputar pada porosnya (spin)
⇒ membentuk medan magnet yang berputar ⇒ penempatan di dalam suatu medan magnet (Bo)
menghasilkan putaran presesi yang menyerap di daerahgelombang radio
⇒ frekuensi presesi dinyatakan oleh:
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Proses terjadinya resonansi?
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When molecules containing hydrogen atoms are placed in an external magnetic field ; the magnetic moment of each proton nucleus aligns itself in one of two different orientations:
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• The parallel protons absorb energy (radio waves) and the magnetic moment turn around (flip) to the high energy antiparallel state (Resonance)
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2 Cara agar terjadi resonansi?
Bo tetap, frekuensi radiasi elektromagnetik diubah - ubah
frekuensi radiasi elektromagnetik
tetap, Bo diubah – ubah sampai
dicapai resonansi,
Lebih memuaskan
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Bentuk spektrum NMR?
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–The spectrum is measured on a delta (d) scale in units of parts per million (ppm)
–Lower frequency is to the left in the spectrum; these absorptions are said to be downfield
–Higher frequency is to the right in the spectrum: these absorptions are said to be upfield
–The small signal at d 0 corresponds to an internal standard called tetramethylsilane (TMS) used to calibrate the chemical shift scale
–The number of signals in the spectrum corresponds to the number of unique sets of protons
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Pergesaran Kimia?
Perbandingan antara letak resonansi suatu proton tertentu dengan letak
resonansi proton standar
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• Chemical Shift• Chemical shifts are measured in relation to the
internal reference tetramethylsilane (TMS)– The protons of TMS are highly shielded because of the
strong electron donating capability of silicon
• The d scale for chemical shifts is independent of the magnetic field strength of the instrument (whereas the absolute frequency depends on field strength)
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Ada apa dengan TMS?
1. TMS mempunyai dua belas proton yang setara kimia,karenya memberikan satu puncak tunggal
2. TMS merupakan cairan yang volatil, dapat ditambahkan dalam jumlah sedikit pada larutan sampel dalam pelarutnya, sampel dapat diperoleh kembali dengan menguapkan pelarutnya
3. Proton pada hampir semua senyawa organik mengalami resonansi pada medan yang lebih rendah daripada proton TMS
4. TMS bersifat inert dan tidak larut dalam air
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Faktor yang mempengaruhi pergesaran kimia?
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Faktor intramolekular1. Efek induksi2. Efek anisotropi3. Efek mesomeri
Faktor intermolekuler4. Ikatan hidrogen5. Temperatur6. Pelarut
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Fields induced by sigma bonds
• The induced field from circulating sigma bond electrons opposes Ho in the vicinity of proton
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• A proton that is bonded to the same carbon as an electronegative atom is more deshielded than proton on other carbons. (Inductive Effect)
• H3C-F H3C-ClH3C-Br H3C-I
4.3d 3.0d 2.7d 2.1d
Increased shielding of H
C FH
HH
F causes a decrease ine density around each atom
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The inductive effect
CH
HH
CH
HCH
HX effect of X is important
in decreasing e densityaround this proton
effect of X is oflittle importancein decreasing e density aroundthis proton
Si
CH3
CH3
CH3
CH3
greater e density on H:highly shielded
Tetramethylsilane(TMS)
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Summary of induced field effects
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Equivalent and nonequivalent protons
MENGHITUNG PROTON
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CH3CH2OCH2CH3
six equivalent protons
four equivalent protons
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CCH3
CH3H
Br six equivalent protons
CH3
CH3
CH3 Br six equivalent protonstwo
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Spin-spin coupling
• Protons that split each other signals are said to have undergone spin-spin coupling
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n+1 Rule
• The number of peaks of a particular proton is equal to number (n) of nonequivalent protons on the adjacent atoms + 1
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Notice:
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Splitting pattern:
• The singletIf no neighboring nonequivalent protons present one single peak (singlet) (S).
eg.CH3 Cl CH3OCCH3
O
CCH3
CH3
Br
CH3 H
HH
H
HH
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The doublet
• If one neighboring nonequivalent proton present two peaks (doublet) (d).
egCH3 C
H
ClCl CH3 C
HCl
CH3
OCH3
HH
CH3
H H
C CHH
ClCl Cl
Cl
equivalent H's => S
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The triplet
• If two neighboring nonequivalent protons present three peaks (triplet) (t).
egCH3CH2Cl
C CHH
ClCl Cl
H
ClCH2CH2OCH3
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The quartet
• If a proton is neighboring to CH3 it will observe 3+1=4 peaks (quartet) (q)
egCH3CH2Cl CH3CHCl2
CH3CH2OCH2CH3
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