Infrared spectroscopy can be used to identify functional groups in molecules based on the vibrational energies of atoms in the molecule when exposed to infrared radiation. Each functional group requires a different energy to vibrate, which causes it to absorb infrared radiation at characteristic wavelengths. The intensity of these absorption peaks indicates the strength of the vibration and can be used to identify functional groups present in an unknown sample.

1. Infrared Spectroscopy
Gugus fungsi adalah atom atau gugusan atom pada suatu molekul yang menentukan sifat
kimia molekul tersebut.
Gugus fungsi diidentifikasi menggunakan teknik spektroskopi, didasarkan pada getaran atom-
atom pada molekul ketika dilewatkan radiasi infra merah.
Radiasi infra merah yang diterima diukur dan ditentukan radiasi yang diserap oleh molekul.
Setiap gugus fungis membutuhkan energi yang berbeda untuk bergetar dan dapat
diidentifikasi. Hal ini akan direkam dalam bentuk peak dalam spektrum.
Gugus fungsi yang menyerap radiasi menunjukkan perubahan momen dipol.
Hal ini antara lain:
- symmetric dan antisymmetric (stretching)
- scissoring dan rocking (bending; in plane)
- wagging dan twisting (bending; out of plane)

2. Intensitas getaran (serapan infra merah pada detektor berbanding terbalik dengan energi yang
diserap untuk menghasilkan getaran).
- Strong (S) peak is tall, transmittance is low (0-35 %)
- Medium (M) peak is mid-height (75-35%)
- Weak (W) peak is short, transmittance is high (90-75%)
- Broad (BR) this is more for describing a bond that spans many energies

3. Ultimate Spectrum Approach
1. Cek gugus karbonil (C=O)
Strong absorption; region 1820-1660
2. Jika tidak ada gugus karbonil, skip ke nomor 3. Jika ada, cek gugus berikut:
- asam (OH); broad absorption near 3400-2400; usually overlaps C-H
- amida (NH); medium absorption near 3500; sometimes a double peak, equivalent halves
- ester (C-O); strong intensity absorptions near 1300-1000
- anhidrida (have two C=O); absorptions near 1810 and 1760
- aldehida (CH); two weak absorptions near 2850 and 2750
- keton; above 5 choices have been eliminated
3. If C=O is absent
Alkohol; cek OH
Fenol; broad absorption near 3400-2400; confirm this by finding C-O near 1300-1000
Amina (NH); medium absorptions(s) near 3500
Eter; cek C-O (and absence of OH) near 1300-1000
4. Double Bonds and/or Aromatic Rings
- C=C is a weak absorption near 1650
- medium to strong absorptions in the region 1650-1450 often imply an aromatic ring
- confirm the above by consulting the CH region; aromatic and vinyl CH occurs to the left
of 3000 (aliphatic CH occurs to the right of this value)
5. Triple Bonds
- C≡N is a medium, sharp absorption near 2250
- C≡C is a weak but sharp absorption near 2150
- Check also for acetylenic CH near 3300
6. Nitro Groups
- two strong absorptions at 1600-1500 and 1390-1300
7. Hydrocarbons
- none of the above are found
- major absorptions are in CH region near 3000
- very simple spectrum, only other absorptions near 1450 and 1375