Lab 3 IR and NMR workshop PDF

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Lab 3 IR and NMR workshop...

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2/19/20 Lab 3: IR and NMR Workshop Introduction: Nuclear Magnetic Resonance (NMR) and Infrared Spectroscopy (IR) are both techniques used in the laboratory to determine the structure and functional groups of chemical compounds. IR specifically is used to identify functional groups and can be helpful when analyzing the special arrangement of hydrogens in molecules with NMR. NMR observes interactions of nuclear spins and measures them in the presence of a powerful magnetic field. In this experiment, the nuclear spin of H1 protons will be measured in NMR and various factors can shift or split these protons. In continuation from Experiment 2, the products of from the ethyl 3- hydroxy butanoate of the yeast reaction of ethyl acetoacetate will be analyzed through 2 NMR techniques. The first technique determines the optical purity of enantiomers when ethyl 3- hydroxy butanoate is reacted with chiral shift reagent. The second technique determines the optical purity of enantiomers when ethyl 3hydroxy butanoate is reacted with (S)-(+ )-α –methoxyphenyl acetic acid using dicyclohexylcarbodiimide (DCC) to create diastereomeric ester pair. The two NMR’s yielded from both techniques will be analyzed and optical purity of products will be deduced for each technique. Furthermore, 3 additional unknown NMR’s and IR’s will be examined, and the structure of the compounds will be extracted to find the identity of the unknown compounds. Methods and Materials: Technique 1 was performed by reacting ethyl-3-hydroxybutanoate with t r i s[ 3 ( h e p t a flu or o pr o p y l -h y dr o x yme t h y l e ne ) c a mp h or a t o] e u r op i u m( I I I )c h i r a l s h i f tr e a g e n ta n dNMRi s o bt a i ne das described in Pavia, Lampman, Kriz and Engel, A Small Scale Approach to Organic Laboratory Techniques, Fourth Edition, Cengage Learning, 2015, pp 230-235. Technique 2 was performed by reacting ethyl-3-hydroxybutanoate with with (S)-(+ )-α –methoxyphenylacetic acid using dicyclohexylcarbodiimide (DCC) to form a diastereomeric ester pair and NMR is obtained as described in the lab manual (pp 19) Results and observations: Technique 1: ethyl-3-hydroxybutanoate reacted with chiral shift reagent: Figure 1: NMR of ethyl-3-hydroxybutanoate before reacting with chiral reagent:

Ha and Hb protons in the 1.2 – 1.3 ppm region

Figure 2: Up close NMR of Ha and Hb in ethyl-3-

hydroxy butanoate reactant

Ha = doublet most up field Hb = Triplet more downfield

Figure 3: ethyl-3-hydroxybutanoate after reaction with chiral shift reagent

After adding chiral shift reagent, chemical shift occurred, shifting hydrogens peaks downfield 1.3 – 1.4 ppm region. Ha became more downfield than Hb. Ha is a doublet of doublets due to mixture of enantiomers in product. Depending on intensity of each peak, were able to identify percentage of each enantiomer. Integration values for Ha: 1 . 41 2a n d1 . 39 1we r ef r o mSe n a nt i ome r 1 . 40 5a n d1 . 38 4we r ef r o mRe n a nt i ome r Hbi sad ou bl e to ft r i p l e t sd uet omi xt u r eo f e n a n t i o me r si npr o du c t I nt e g r a t i onv al ue sf o rHb: 1 . 31 6, 1 . 29 3, a n d1 . 26 9we r ef r o mRe n a n t i ome r 1 . 32 2, 1 . 29 8, 1 . 27 4we r ef r o m Se na n t i ome r

To find optical purity of each enantiomer present in reacted ethyl-3-hydroxybutanoate with chiral shift reagent, the two methyl group regions of the product are observed, and integration values are calculated. From the integration values, a ratio was obtained and from that ratio, percentage of each enantiomer present is able to be calculated.

Technique 2: ethyl-3-hydroxybutanoate reacted with (S)-(+ )-α –methoxyphenylacetic acid using dicyclohexylcarbodiimide (DCC) to form a diastereomeric ester pair Figure 4: NMR of (S,S) Diastereomer

Chemical shift: 1.1 ppm – 1.4ppm Hb is triplet: ~1.1 ppm Ha is doublet: ~ 1.3 ppm

Figure 5: NMR of (S,R) Diastereomer

Both Ha and Hb had no chemical shift. Multiplet peaks around 1.2 ppm

To find optical purity of each isomer in the reaction with DCC, integration values are obtained, and integration ratios are calculated. From the ratios, percentages of each isomer can be obtained. Treatment of Results: IR and NMR 12:

Unknown #12 Structure:

IR Data for Unknown # 12 (liquid film) IR absorption (cm-1) 2850-2960 ~1645 ~1050 3600-3200 ~1700

Intensity/ Description strong/sharp medium/sharp medium/sharp Strong/ broad medium/sharp

Assigned Functional group Alkane sp3 C-H C=C Alkene C-O -OH alcohol of acid C=O carbonyl

NMR Data for Unknown # 12 (90 MHz, CDCl3) Chemical Shift (ppm) ~4 ~7.0-7.1 ~7.5-7.6 ~8.1 10.2-10.3

No. of Protons

multiplicity

Assigned Proton(s)

3 1 2 1 1

singlet multiplet multiplet multiplet multiplet

f c d,e b a

Unknown #28:

propylbenzene

IR and NMR 28

IR Data for Unknown # 28 (liquid film) IR absorption (cm-1) 2960-2850 3030-3050

Intensity/Description strong/sharp medium/sharp

Assigned Functional group Alkane sp3 carbon aromatic

NMR Data for Unknown # 28 (90 MHz, CDCl3) Chemical Shift (ppm) 0.9-1 1.55-1.65 2.5-2.6 ~7.1-7.4

Unknown # 34 Structure:

No. of Protons

multiplicity

Assigned Proton(s)

3 2 2 5

triplet multiplet triplet multiplet

d c b a

IR and NMR 34:

IR Data for Unknown # 34 C6H14O (liquid film) IR absorption (cm-1) ~2850-2960 ~1030

Intensity/Description strong/sharp Strong/sharp

Assigned Functional group Alkane Ether R-O-R

NMR Data for Unknown # 34 (90 MHz, CDCl3) Chemical Shift (ppm) ~1.1-1.2 ~3.6 – 3.7

No. of Protons

multiplicity

Assigned Proton(s)

12 2

doublet septet

a b

Discussion and Conclusion: In part 1 of this lab, two NMR techniques were used to determine the optical purity of enantiomeric and diastereomeric isomers. The first technique required the reaction of ethyl 3hydroxy butanoate with chiral shift reagent to yield R and S enantiomers. The effect of this was seen on the with the methyl groups on the NMR spectrum by yielding doublets of doublets and doublets of triplets as seen in Figure 3. From there integration values can be calculated and percentages of each enantiomer can be determined. For technique 2, the reaction of ethyl 3- hydroxy butanoate with (S)-(+ )-α –methoxyphenylacetic acid and dicyclohexylcarbodiimide (DCC) formed a diastereomeric ester pair. DCC reagent formed an ester bond between the carboxylic acid and hydroxy group giving diastereomeric products. This allowed for two products to be formed one with SS configuration and one with S,R configuration. Both had separate NMR’s conducted. The S,S isomer’s Ha on the S configuration had a small chemical downfield because in the S configuration is was closer to the electronegative oxygen. Optical purity was able to be determined for each R configuration and S configuration within both diastereomers through integration value ratios and calculations. In part 2, unknown structures were identified from IR and NMR spectrums provided. Functional groups were derived from IR while special arrangement was derived from NMR. The first unknown 12 had sp3 hybridized carbons within the 3000 cm-1 to 2850 cm-1 stretch. This indicated the presence of a methyl group. There was also presence of a broad hydroxy peak. Then there was a carbonyl peak at about 1700 cm-1 region and a alkene peak at about 1645 cm-1. There was also the presence of. C-O peak at around 1230. Having carbonyl and hydroxy peaks signified presence of an carboxylic acid. There was also a C-O bond present from the peak observed in the ~1230 region that signified a possible ether. From the NMR, the structure was deduced by the multiplets seen in the 7-8 region which signified the presence of benzene. The coupling pattern was ortho based on the position of hydrogens on the benzene. There was also a peak in the 10.2-10.3 region signifying the presence of carboxylic acid. There was a singlet at 4 ppm with an integration of 3H which represented a CH3 group connected to an electronegative oxygen which caused a chemical shit to 4 ppm resulting in an ether being present. From there, the structure was easily determined. For unknown 28, it was identified as C9H12. The IR had high frequency absorptions in the 3030 – 3050cm-1 region signifying the presence of sp2 C-H bonds within an aromatic. Absorption frequencies of 2850-2960 cm-1 signified the presence of sp3 C-H bonds. The IR functional groups coincided with the NMR multiplet at about 7.1-7.4 ppm which signified presence of benzene ring. It had an integration value of 5 signifying that 5 hydrogens were around the ring, leaving one open spot for an alkyl chain on benzene ring. There was a multiplot with an integration of 2 at around 1.5-1.65ppm signifying that CH2 has to be in the middle of two chemically non-equivalent hydrogens. This CH2 group was in between a CH2 and CH3, which are both chemically inequivalent causing complex splitting to have occurred. The triplet with 2.5-2.6 ppm and integration value of 2 had a chemical shift because it was the closest to the benzene ring. The first triplet with integration of 3 is most up field because it’s a methyl group furthest away from benzene so benzene ring doesn’t have much of an effect on its chemical shift.

For unknown 34, the molecular formula of C6H14O was given. The IR yielded two absorption frequencies. One ranging between about 2850-2960 cm-1 indicating the presence of Sp3. Hybridized carbons. The second peak that helped identify the ether functional group was a peak around the 1030 region. This demonstrated that an alkyl ether was present. For the NMR 2 signals were observed signifying 2 different types of hydrogens were present. The first peak around the 1.1 ppm region was identified as a doublet, with one neighboring proton. This first peak had to be CH3 but had an integration value of 12 so it was evident that 4 equivalent CH3 had to be present. Knowing that an ether was present, the ether was drawn with 2 CH3 groups on each side. Then as a trial and error 2 hydrogens were added to the carbon on each side connected to oxygen and two methyl groups and these hydrogens coincided with the 2H integration, along with the septet multiplicity that gave 6 neighboring hydrogens....