(1) Calculate the unsaturation formula according to the molecular formula: unsaturation ω=n4+1+ (n3-n1) /2, where: n4: number of atoms with valence 4 (mainly C atoms), n3: number of atoms with valency 3 (mainly N atoms), n1: number of atoms with valence 1 (mainly H, X atoms)
(2) Analyze C-H telescopic vibration absorption in the 3300~2800cm-1 region; using 3000 cm-1 as the boundary: C-H telescopic vibration absorption of unsaturated carbon above 3000cm-1, possibly alkene, aromatic compounds; while below 3000cm-1 is generally saturated C-H telescopic vibration absorption;
(3) If absorption is slightly higher than 3000 cm-1, the characteristic peak of telescopic vibration absorption of unsaturated carbon-carbon bonds should be analyzed in the 2250 to 1450 cm-1 frequency region, where acetylene: 2200 to 2100 cm-1, ene: 1680 to 1640 cm-1 aromatic ring: 1600,1580, 1500, 150 cm-1 if determined as an ene or aromatic compound, the fingerprint region, that is, the frequency region of 1000 to 650 cm-1, to determine the number and position of substituents (transverse, adjacent, between, pair);
(4) After the carbon framework type is determined, the functional group of the compound is determined based on absorption characteristics;
(5) When analyzing, care should be taken to link the relevant peaks describing each functional group to accurately determine the presence of functional groups, such as the three peaks of 2820, 2720, and 1750-1700 cm-1, indicating the presence of aldehyde groups.
Remember your health
1. Alkanes: C-H expansion vibration (3000-2850cm-1) C-H bending vibration (1465-1340cm-1). Generally, saturated hydrocarbon C-H expansion is below 3000 cm-1, close to 3000 cm-1 frequency absorption.
4. Aromatics: C-H telescopic vibration 3100~3000cm-1 on the aromatic ring, C=C skeleton vibration 1600~1450cm-1, C-H external bending vibration 880~680cm-1.
Important characteristics of aromatic hydrocarbons: 4 peaks of varying intensity may occur at 1600, 1580, 1500, and 1450cm-1. The external bending of the C-H surface absorbs 880 to 680 cm-1, and changes depending on the number and position of substituents on the ephenyl ring. In infrared spectrum analysis of aromatic compounds, isomers are commonly used to identify isomers.
5. Alcohol and phenol: The main characteristic absorption is the telescopic vibration absorption of O-H and C-O; the telescopic vibration of free hydroxyl O-H: 3650 to 3600 cm-1, which is a sharp absorption peak; intermolecular hydrogen bond O-H telescopic vibration: 3500 to 3200 cm-1, which is a wide absorption peak; C-O telescopic vibration: 1300~1000cm-1, O-H external bending: 769-659cm-1
6. Ether characteristics absorption: 1300 to 1000 cm-1 telescopic vibration, fatty ether: 1150 to 1060 cm-1 a strong absorption peak aromatic ether: 1270 to 1230 cm-1 (for Ar-O expansion), 1050 to 1000 cm-1 (for R-O expansion)
7. Aldehyde and ketone: characteristic absorption of aldehyde: 1750~1700cm-1 (C=O expansion), 2820, 2720cm-1 (aldehyde group C-H expansion) Fatty ketone: 1715cm-1, strong C=O telescopic vibration absorption. If carbonyl is conjugated with an alkene bond or aromatic ring, the absorption frequency will decrease
9. Ester: C=O absorption band of saturated fatty acid esters (excluding formates): 1750~1735cm-1 region saturated ester C-O band: 1210~1163cm-1 region is strong absorption
Infrared can be divided into the far, middle, and near, medium red characteristic fingerprint regions. The border is about 1300. Note the differences in the horizontal axis division. If you look at the picture, you need to know the infrared meter to understand the solid state of liquid gas. Sample source sample preparation method, physico-chemical properties are multi-linked.
Learn saturated hydrocarbons first, and look at peak shapes below 3,000.
2960 and 2870 are methyl, 2930, and 2850 methylene peaks. 1470 hydrocarbon bending, 1380 methyl display. Two methyls are the same carbon, two and a half parts of 1,380. The 720 swings inside the surface, and long chains of methylene are also recognizable.
Olehydride stretches over 3,000, excluding frequency doubling and halocarbons. This peak of terminal olefins is strong; only monohydrogen is not significant. Compounds, and bond deviations, ~1650 will occur.
Olehydride is easily deformed outside the surface, and there are strong peaks below 1000. 910 terminal hydrogen, and one hydrogen 990.
Cis dihydrogen 690, trans moved to 970; monohydrogen peaked at 820, interfering with cis difficult to determine.
Hydrogen alkyne stretches three thousand three thousand three, and the peak is large and sharp. Three bonds stretch two thousand two, and hydrogen alkyne swings 68.
Aromatic hydrocarbon respiration is very special, 1600 to 1430, 1650 to 2000, and the substitution methods are clearly distinguished. 900 to 650, aromatics are determined by bending the outside of the surface. Pentahydrogen absorption has two peaks, 700 and 750; tetrahydrogen is only 750, and dihydrogen is adjacent to 830; three peaks replace three peaks. Isolated hydroalcoholphenol hydroxyl groups easily associate at 700, 780, and 880, and there are strong peaks at 333 locations. C-O stretches and absorbs a lot, and it is easy to distinguish between Pak Zhong Shu Ji. 1050 shows primary alcohol, 1100 is middle, 1150 tertiary alcohol is present, and 1230 is phenol.
1110 ether chain extension, be careful to exclude ester alcohol. If it is closely connected to the pi bond, the two absorptions should be accurate. 1050 has a symmetric peak, and 1250 has an opposite symmetry. If the benzene ring has a methoxy group, the hydrocarbon stretches 2820. The methylene dioxane ring has a strong peak at 930, ethylene oxide has three peaks, and the 1,260 ring vibrates. It is opposed to around 900. It is most characteristic around 800. acetone, special ether, 1110 non-acetone. Acid anhydrides also have C-O bonds. There is a difference between open chain cyclic anhydrides. The open chain peak is 1,100, and the cyclic anhydride moves to 1250.
The carbonyl group stretches 17,2720 fixed aldehyde groups. The number of waves of the absorption effect is high, and the conjugation shifts to a lower frequency. The tension causes rapid vibration, which can be compared to a double button outside the ring.
From 25 to 3000, the hydrogen bond peak of carboxylic acid is wide, 920, with a blunt peak. The carboxyl group can be defined as dimeric acid. Acid anhydrides are combined in 18, and the double peaks are 60 strictly separated. The high frequency of chain anhydrides is strong, and the high frequency of cyclic anhydrides is weak. Carboxylates, conjugates, and carbonyl stretches out to double peaks, 1600 antisymmetric, and 1400 symmetric peaks.
1740 carbonyl ester. For what acid, you can see the carbon oxygen exhibition. 1180 formate, 1190 is propionic acid, 1220 acetate, 1250 aromatic acid. 1600 rabbit ear peak, often phthalic acid.
Nitrogen and hydrogen stretch three thousand four, and each peak of hydrogen is very distinct. Carbonyl stretch amide I, 1660 has a strong peak; N-H modified amide II, 1600 decibels. Primary amines are high in frequency and easy to overlap; secondary acyl solid state 1550; carbon and nitrogen stretch amide III, strong peak of 1400.
Amine tips are often interfered with. N-H stretches three thousand three, tertiary amines have no peak secondary amines, and primary amines have small spikes. 1600 hydrocarbon bends, aromatic secondary amine 1,5 bias. Shake the surface for about 800 to determine if it is best to turn it into salt. Stretching and bending are close to each other. Primary amine salts have a peak width of 3,000; secondary amine salts and tertiary amine salts can be distinguished above 2,700; imine salts are even worse; they can only be seen around 2000.
Nitro contraction absorption is large, and the connected groups can be clarified. 1350 and 1500 are divided into symmetric objections. Amino acid, internal salt, wide peak shape from 3100 to 2100. 1600, 1400 acid root exhibitions, 1630, 1510 hydrocarbon bends. hydrochloride, carboxyl group, sodium salt protein three thousand three.
The mineral composition is mixed, and the vibrational spectrum is far at the red end. Ammonium salts are simpler, have fewer and wider absorption peaks. Pay attention to hydroxyl water and ammonium. First, remember a few common salts: 1100 is sulfuric acid, 1380 nitrate, and 1450 carbonate. Look at phosphoric acid for about 1,000. Silicate, a wide peak, 1000 is really spectacular.
With diligent study and practice, infrared spectroscopy is not difficult.
(1) Calculate the unsaturation formula according to the molecular formula: unsaturation ω=n4+1+ (n3-n1) /2, where: n4: number of atoms with valence 4 (mainly C atoms), n3: number of atoms with valency 3 (mainly N atoms), n1: number of atoms with valence 1 (mainly H, X atoms)
(2) Analyze C-H telescopic vibration absorption in the 3300~2800cm-1 region; using 3000 cm-1 as the boundary: C-H telescopic vibration absorption of unsaturated carbon above 3000cm-1, possibly alkene, aromatic compounds; while below 3000cm-1 is generally saturated C-H telescopic vibration absorption;
(3) If absorption is slightly higher than 3000 cm-1, the characteristic peak of telescopic vibration absorption of unsaturated carbon-carbon bonds should be analyzed in the 2250 to 1450 cm-1 frequency region, where acetylene: 2200 to 2100 cm-1, ene: 1680 to 1640 cm-1 aromatic ring: 1600,1580, 1500, 150 cm-1 if determined as an ene or aromatic compound, the fingerprint region, that is, the frequency region of 1000 to 650 cm-1, to determine the number and position of substituents (transverse, adjacent, between, pair);
(4) After the carbon framework type is determined, the functional group of the compound is determined based on absorption characteristics;
(5) When analyzing, care should be taken to link the relevant peaks describing each functional group to accurately determine the presence of functional groups, such as the three peaks of 2820, 2720, and 1750-1700 cm-1, indicating the presence of aldehyde groups.
Remember your health
1. Alkanes: C-H expansion vibration (3000-2850cm-1) C-H bending vibration (1465-1340cm-1). Generally, saturated hydrocarbon C-H expansion is below 3000 cm-1, close to 3000 cm-1 frequency absorption.
2. Olefin: Olefin C-H expansion (3100~3010cm-1), C=C expansion (1675~1640 cm-1), olefin C-H external bending vibration (1000~675cm-1).
3. Alkynes: Alkynes C-H telescopic vibration (around 3300cm-1), three-bond telescopic vibration (2250 to 2100 cm-1).
4. Aromatics: C-H telescopic vibration 3100~3000cm-1 on the aromatic ring, C=C skeleton vibration 1600~1450cm-1, C-H external bending vibration 880~680cm-1.
Important characteristics of aromatic hydrocarbons: 4 peaks of varying intensity may occur at 1600, 1580, 1500, and 1450cm-1. The external bending of the C-H surface absorbs 880 to 680 cm-1, and changes depending on the number and position of substituents on the ephenyl ring. In infrared spectrum analysis of aromatic compounds, isomers are commonly used to identify isomers.
5. Alcohol and phenol: The main characteristic absorption is the telescopic vibration absorption of O-H and C-O; the telescopic vibration of free hydroxyl O-H: 3650 to 3600 cm-1, which is a sharp absorption peak; intermolecular hydrogen bond O-H telescopic vibration: 3500 to 3200 cm-1, which is a wide absorption peak; C-O telescopic vibration: 1300~1000cm-1, O-H external bending: 769-659cm-1
6. Ether characteristics absorption: 1300 to 1000 cm-1 telescopic vibration, fatty ether: 1150 to 1060 cm-1 a strong absorption peak aromatic ether: 1270 to 1230 cm-1 (for Ar-O expansion), 1050 to 1000 cm-1 (for R-O expansion)
7. Aldehyde and ketone: characteristic absorption of aldehyde: 1750~1700cm-1 (C=O expansion), 2820, 2720cm-1 (aldehyde group C-H expansion) Fatty ketone: 1715cm-1, strong C=O telescopic vibration absorption. If carbonyl is conjugated with an alkene bond or aromatic ring, the absorption frequency will decrease
8. Carboxylic acid: Carboxylic acid dimer: 3300~2500cm-1 wide and strong O-H telescopic absorption 1720-1706cm-1 C=O telescopic absorption 1320-1210cm-1 C-O telescopic absorption, 920cm-1 out-of-plane bending vibration of bonded O-H bonds
9. Ester: C=O absorption band of saturated fatty acid esters (excluding formates): 1750~1735cm-1 region saturated ester C-O band: 1210~1163cm-1 region is strong absorption
10. Amine: N-H telescopic vibration absorption 3500~3100 cm-1; C-N telescopic vibration absorption 1350~1000 cm-1; N-H deformation vibration equivalent to CH2 scissor vibration absorption: 1640~1560cm-1; external bending vibration absorption 900~650 cm-1.
11. Nitrile: three-bond telescopic vibration region with weak to moderate absorption aliphatic nitrile 2260-2240cm-1 aromatic nitrile 2240-2222cm-1
12. Amide: 3500-3100cm-1 N-H telescopic vibration
1680-1630cm-1 C=O telescopic vibration
1655-1590cm-1 N-H bending vibration
1420-1400cm-1 C-N telescopic
13. Organic halides: aliphatic C-X expansion: C-F 1400-730 cm-1, C-Cl 850-550 cm-1, C-Br 690-515 cm-1, C-I 600-500 cm-1
Infrared Reading Song
Infrared can be divided into the far, middle, and near, medium red characteristic fingerprint regions. The border is about 1300. Note the differences in the horizontal axis division. If you look at the picture, you need to know the infrared meter to understand the solid state of liquid gas. Sample source sample preparation method, physico-chemical properties are multi-linked.
Learn saturated hydrocarbons first, and look at peak shapes below 3,000.
2960 and 2870 are methyl, 2930, and 2850 methylene peaks. 1470 hydrocarbon bending, 1380 methyl display. Two methyls are the same carbon, two and a half parts of 1,380. The 720 swings inside the surface, and long chains of methylene are also recognizable.
Olehydride stretches over 3,000, excluding frequency doubling and halocarbons. This peak of terminal olefins is strong; only monohydrogen is not significant. Compounds, and bond deviations, ~1650 will occur.
Olehydride is easily deformed outside the surface, and there are strong peaks below 1000. 910 terminal hydrogen, and one hydrogen 990.
Cis dihydrogen 690, trans moved to 970; monohydrogen peaked at 820, interfering with cis difficult to determine.
Hydrogen alkyne stretches three thousand three thousand three, and the peak is large and sharp. Three bonds stretch two thousand two, and hydrogen alkyne swings 68.
Aromatic hydrocarbon respiration is very special, 1600 to 1430, 1650 to 2000, and the substitution methods are clearly distinguished. 900 to 650, aromatics are determined by bending the outside of the surface. Pentahydrogen absorption has two peaks, 700 and 750; tetrahydrogen is only 750, and dihydrogen is adjacent to 830; three peaks replace three peaks. Isolated hydroalcoholphenol hydroxyl groups easily associate at 700, 780, and 880, and there are strong peaks at 333 locations. C-O stretches and absorbs a lot, and it is easy to distinguish between Pak Zhong Shu Ji. 1050 shows primary alcohol, 1100 is middle, 1150 tertiary alcohol is present, and 1230 is phenol.
1110 ether chain extension, be careful to exclude ester alcohol. If it is closely connected to the pi bond, the two absorptions should be accurate. 1050 has a symmetric peak, and 1250 has an opposite symmetry. If the benzene ring has a methoxy group, the hydrocarbon stretches 2820. The methylene dioxane ring has a strong peak at 930, ethylene oxide has three peaks, and the 1,260 ring vibrates. It is opposed to around 900. It is most characteristic around 800. acetone, special ether, 1110 non-acetone. Acid anhydrides also have C-O bonds. There is a difference between open chain cyclic anhydrides. The open chain peak is 1,100, and the cyclic anhydride moves to 1250.
The carbonyl group stretches 17,2720 fixed aldehyde groups. The number of waves of the absorption effect is high, and the conjugation shifts to a lower frequency. The tension causes rapid vibration, which can be compared to a double button outside the ring.
From 25 to 3000, the hydrogen bond peak of carboxylic acid is wide, 920, with a blunt peak. The carboxyl group can be defined as dimeric acid. Acid anhydrides are combined in 18, and the double peaks are 60 strictly separated. The high frequency of chain anhydrides is strong, and the high frequency of cyclic anhydrides is weak. Carboxylates, conjugates, and carbonyl stretches out to double peaks, 1600 antisymmetric, and 1400 symmetric peaks.
1740 carbonyl ester. For what acid, you can see the carbon oxygen exhibition. 1180 formate, 1190 is propionic acid, 1220 acetate, 1250 aromatic acid. 1600 rabbit ear peak, often phthalic acid.
Nitrogen and hydrogen stretch three thousand four, and each peak of hydrogen is very distinct. Carbonyl stretch amide I, 1660 has a strong peak; N-H modified amide II, 1600 decibels. Primary amines are high in frequency and easy to overlap; secondary acyl solid state 1550; carbon and nitrogen stretch amide III, strong peak of 1400.
Amine tips are often interfered with. N-H stretches three thousand three, tertiary amines have no peak secondary amines, and primary amines have small spikes. 1600 hydrocarbon bends, aromatic secondary amine 1,5 bias. Shake the surface for about 800 to determine if it is best to turn it into salt. Stretching and bending are close to each other. Primary amine salts have a peak width of 3,000; secondary amine salts and tertiary amine salts can be distinguished above 2,700; imine salts are even worse; they can only be seen around 2000.
Nitro contraction absorption is large, and the connected groups can be clarified. 1350 and 1500 are divided into symmetric objections. Amino acid, internal salt, wide peak shape from 3100 to 2100. 1600, 1400 acid root exhibitions, 1630, 1510 hydrocarbon bends. hydrochloride, carboxyl group, sodium salt protein three thousand three.
The mineral composition is mixed, and the vibrational spectrum is far at the red end. Ammonium salts are simpler, have fewer and wider absorption peaks. Pay attention to hydroxyl water and ammonium. First, remember a few common salts: 1100 is sulfuric acid, 1380 nitrate, and 1450 carbonate. Look at phosphoric acid for about 1,000. Silicate, a wide peak, 1000 is really spectacular.
With diligent study and practice, infrared spectroscopy is not difficult.
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