FTIR - FTIR lab report PDF

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FTIR lab report...

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Purpose The purposes of this experiment are; 1) to demonstrates the different methods of sample preparation for IR analysis 2) to identify functional groups from infrared spectra 3) to determine the structure of an unknown component from the functional group 4) to illustrate the effect of substituents and conjugation of a molecule Procedure Thermo Nicolet Avatar 360 spectrometer was used for TFIR experiment. Carver press was used for preparing potassium bromide pallet Liquid Samples NaCl cell (0.5cm) was inserted to acquire a background spectrum. Two drops of CCl4 sample was dropped on the NaCl window, and IR spectrum was collected. Empty KBr cell (0.5cm) was used as a reference for acetone sample. When the background spectrum was collected, two drops of acetone sample was dropped on the KBr window, and IR spectrum of acetone was collected. Other liquid samples in the following table were prepared to collect each IR spectrum. KBr cell was used as a reference for each sample. Table 1. Liquid samples according to their groups

Group 1

Group 2

Group3

Group4

Group 5

Acetone Benzaldehyde Acetophenone iso-Butyraldehyde Acetaldehyde

N-Butyl alcohol tert-Butyl alcohol sec-Butyl alcohol Benzyl alcohol

Nitrobenzene Benzonitrile Benzene

Ethyl benzene Ethyl acetate

Acetanilide

Solid Samples – Pallet method Benzoic acid sample (1.6 mg) was measured and delivered into an agate mortar. The solid sample in the mortar was ground for about 15 minutes. Solid dry KBr (200.0 mg) was put into the mortar and crushed to beach-sand size. The mixture of the sample and KBr was mixed well and placed in between the anvil of the die assembly. The die assembly was placed in the center of

Carver hydraulic press. The die was pressed for 5 minutes at a pressure of 8 tons. Air was used as a reference when the sample pallet was ready. The sample was run through the IR spectrometer to collect the infrared spectrum. Solid Samples – Solution method Benzoic acid sample (61.1 mg) was dissolved in 5 mL of CCl4. Empty KBr cell (0.5 cm) was used as the reference. The sample was run a few times to collect IR spectrum. The spectrum of Aldehydes and Ketones The infrared spectrum of following each sample was collected to compare the carbonyl absorption; benzaldehyde, cinnamaldehyde, iso-butyraldehyde, benzophenone, cyclohexanone, and acetophenone. For liquid samples, KBr cell (0.5 cm) was used as the reference and window, and pallet method was applied for the solid samples. Data and Result Experiment 8-1 The IR spectrum of carbon tetrachloride shows medium stretches at 800 cm-1 and 1100 cm-1 and a weak stretch at around 3000 cm-1. This result gives quite a low matching percentage with the library data of 55.75 %. Most of the IR spectra of group 1 show a high matching percentage with the library data. The infrared spectrum of iso-butyraldehyde depicted a lower carbonyl stretch, and wider and higher O-H band stretch compared to the library data. The KBr pallet of benzophenone sample had low accuracy with a slope showing in the infrared spectrum. The IR spectrum of acetaldehyde has weak stretches in the entire region and an O-H stretch which indicate the possibility of oxidation. Two different method used for benzoic acid has similar IR spectra. The spectrum from the pallet method has overall lower % transmittance than the spectrum from the solution method. The solution has a sharp and strong stretch at 800 cm-1 which are from the solvent. Other than these differences, both data show fairly consistency in significant absorption regions. Group 2 and group 3 has a major difference in the O-H stretch. Compounds of group 2, alcohol compounds, has a wide and strong stretches caused by the O-H bond. Compounds of group 3, the benzene compounds, shows noticeable sharp and narrow stretches. Especially, all the benzene compounds have C-H aromatic stretch at the region around 3100 cm-1 and C=O stretch at the region around 1500cm-1. The IR spectrum of Group 4 and 5 compounds depict a significant difference at a frequency of

3250 cm-1. The spectrum of acetanilide has a strong stretch at 3250 cm-1 due to the N-H bond while ethyl benzoate has no stretch at the same region. Both spectra have medium and strong stretch at 3000 cm-1 and 1750 – 1700cm-1. The unknown compound shows medium C-H aromatic stretch between 3200 cm-1 and 3100 cm-1. The IR spectrum has a strong C-H methyl stretch at the region of 3000 cm-1. The maximum absorption recorded was a C=O stretch at 1720 cm-1. The IR spectrum gives the unknown identification as methyl benzoate. Table 2. IR Spectra Library Search Results of Samples of experiment 8-1

Compound

Molecular Formula

Match (%)

Library/Compound

Carbon tetrachloride

CCl4

55.75

Carbon tetrachloride

Acetone Methyl ethyl ketone iso-Butyraldehyde Benzaldehyde Acetaldehyde Acetophenone Benzophenone

C3H6O C4H8O C4H8O C7H6O C2H4O C8H8O C13H10O

99.14 93.02 79.51 90.00 54.05 82.89 77.21

Acetone, 99+% 2-Buthanone, 99+% iso-Butyraldehyde, 98% Acetophenone, 99% Poly (vinyl alcohol), 98% Benzaldehyde, 98% Benzophenone, 99%

94.27 78.14 95.20 95.66

1-Butanol. 99+% Benzyl alcohol (+/-)-2-Butanol, 99% 2-methyl-2-prophanol, 99.5%

84.66 94.23 92.92

Benzonitrile, 99+% Nitrobenzene, 99+% Benzene, 99+%

96.00 87.89

Ethyl benzoate, 99+% Ethyl acetate, 99.5+%

Group 1

Group 2 n-Butyl alcohol Benzyl alcohol sec-Butyl alcohol tert-Butyl alcohol

C4H10O C8H8O C4H10O C4H10O

Benzonitrile Nitrobenzene Benzene

C7H5N C6H5NO2 C6H6

Group 3

Group 4 Ethyl benzoate Ethyl Acetate

C9H10O2 C4H8O2

Acetanilide

C8H6NO

83.19

Acetanilide

Benzoic acid (KBr Pallet) Benzoic acid (Solution)

C7H6O2 C7H6O2

87.89 83.19

Benzoic acid, 99+% Acetanilide

Group 5

Unknown

C8H9NO

97.00

Methyl benzoate, 99%

Experiment 8-2 The carbonyl stretch of aldehydes and ketones lowers with the conjugation with double bonds or a benzene ring. Among the aldehydes, iso-butyraldehyde with no double bond and benzene ring shows the highest stretching frequency of 1735 cm-1. Benzaldehyde with three double bonds follows with the frequency of 1700 cm-1 and cinnamaldehyde with four double bonds of 1678 cm-1. Ketones also show the same tendency with cyclohexane with the highest frequency of 1715 cm-1 and benzophenone with the lowest frequency of 1652 cm-1. Table 3. Experiment 8-2: Structures and Carbonyl Absorption Frequencies of Aldehydes and Ketones

Compound/structure

Absorbing Region

Number of Double Bonds

Benzaldehyde Cinnamaldehyde iso-butyraldehyde Benzophenone Cyclohexanone Acetophenone

1700 cm-1 1678 cm-1 1735 cm-1 1652 cm-1 1715 cm-1 1682 cm-1

3 4 0 6 0 3

Conclusion and Results The IR spectrum of group 1 through 5 provides successful identification of different functional groups. While carbon tetrachloride shows simple spectrum with C-Cl stretch, compounds of group 1 show several stretches from C-H, C-O, C=O, and C-C bond. The IR spectrum of isobutyraldehyde has a wide O-H stretch which may indicate the oxidation or contamination of the sample. It was also not easy to collect volatile substances such as carbon tetrachloride and acetaldehyde. Both spectra of CCl4 and acetaldehyde show a similar problem of considerably low stretches. The problem of volatile solvent was also addressed with the solution method for the solid benzoic acid sample. The spectrum for sample solution had to collect a few times to acquire clear, and the spectrum still contains the stretches from the solvent, CCl4. KBr pellet of benzoic acid was more easy and convenient to prepare while it had shown less transparency than the solution method. The overall percentage transmittance was lower in the pellet method than the solvent method. Comparison of group 2 and 3 provide different abortion behaviors of alcohol and benzene compound. Alcohols have wide and strong O-H stretch while the benzene compounds have sharp and narrow C-H and C=O stretches at 3100 cm-1 and 1500 cm-1. Group 5 compounds have a strong N-H stretch at 3250 cm-1 when the group 4 have no noticeable stretch in the same region. Both group 4 and 5 have medium and strong stretches at 3000 cm-1 and 1750-1700 cm-1. The unknown compound was identified to be methyl benzoate. The conclusion of the experiment 8-2 illustrates the effect of substituents and conjugation on the carbonyl absorption frequencies. As the number of double bond increases, the intensity of the molecule increases so the carbonyl absorption frequency would be lowered.

Pre and post lab questions Prelab Colorimeter

Visible Spectrophotometer

Ultraviolet spectrophotometer

Infrared Spectrophotometer

Source

Incandescent lamp or sunlight

Tungsten or halogen lamp

Deuterium or hydrogen lamp

Nernst glower or Nichrome wire

Monochromator

None or colored filters

Fused silica, quartz prism, or interference filters

Gratings

Gratings or interference wedge/filters

Sample holder

Glass or clear plastic

Quartz or fused silica

L.F., KBr, TIB or TII

NaCl, KBr, TIB or TII

Sample thickness

1-10 cm

1-10 cm

1-10 cm

1-10 cm

Detector

Eye or photo cell

Photocell, Silicon diode, Charge-transfer detector, or phototube

Photographic plate or photomultiplier tube

Photoconductor, thermocouple or bolometer

Recorder

Brain or galvanometer

Signal processor

Signal processor

Signal processor

Wavelength range

400 - 800 nm

390 – 700 nm

160 - 375 nm

800-15000 nm

2−a¿ wavenumber=

1 =2000 cm−1 −4 10 cm 5 µm × 1 µm

c 2.998 ×1010 cm∙ s−1 13 −1 2−b ¿ frequency= = =6 ×10 s λ 10−4 cm 5 µm× 1 µm 2−c ¿ 5 µm ×

10000 Å =5× 104 Å 1 µm

2−d ¿ 5 µm ×

1000 nm =5000 nm 1 µm

3. wavenumber =

1 1 = =3333 cm−1 wavelength( cm ) 1 cm 3333

1 ×10 4 µm 1 cm× =3 µm 3333 1 cm 4. Infrared absorption region of Ester: 5.7 - 5.8 and 7.9 - 9.2

5. A compound exhibited strong absorption at both 6.2 and 6.7 would be an organic acid, O

anhydride or ester with carboxylate

C

–

O

Post lab Experiment 8-1 1. Water soluble solid sample can be prepared for IR using mull technique, pellet method, or film method. Mull technique uses mineral oil such as Nujol with finely ground sample. Mull technique is the fastest and easiest. However, the sample thickness control is not possible, so internal standard is required for quantitative result. It also has the disadvantage of absorption frequency depends on the mineral oil. Pellet technique is one that uses potassium bromide pellet prepared under great pressure. The result of this method may be used for both quantitative and qualitative spectrophotometry. This method is rapid and easy while it is difficult to avoid some moisture pickup and uncertainty caused by the process of producing the pellet. Film technique is one that cut the sample into sheets of suitable thickness, melt the sample to dry it as a film, or evaporate the sample solution to acquire the sample film. Film technique is difficult to process and usually involve the possibility of interference fringes which are recorded as absorption bands. 2. Double beam spectrophotometer measures the ratio of light intensities between the sample and reference at the same time. So, it would not fluctuate in the light source or detector. But it has lower dynamic range than the single beam spectrophotometer and usually larger size the instrument is. Experiment 8-2 1. When the chlorine atom substitutes an alkyl group, the carbonyl stretching frequency would shift up by withdrawing electron. 2. The C=O overtone would be at 3300 cm-1....