SPEKTROMETRI PROTON NMR

OLEH :YUSBARINA, M.Si

JURUSAN P. KIMIA FTK UIN SUSKA RIAU

NMR ?

NUCLEAR MAGNETIC RESONANCEATAU

RESONANSI MAGNET INTI

H-NMR C-NMR

Kegunaan H-NMR?

Memberikan gambaran mengenai :1. Jenis hidrogen2. Jumlah hidrogen3. Lingkungan hidrogen dalam

suatu senyawa

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

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:

Proses terjadinya resonansi?

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:

• The parallel protons absorb energy (radio waves) and the magnetic moment turn around (flip) to the high energy antiparallel state (Resonance)

2 Cara agar terjadi resonansi?

Bo tetap, frekuensi radiasi elektromagnetik diubah - ubah

frekuensi radiasi elektromagnetik

tetap, Bo diubah – ubah sampai

dicapai resonansi,

Lebih memuaskan

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

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)

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

Faktor yang mempengaruhi pergesaran kimia?

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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