NMR Analysis - Predicting a Structure Based on NMR and IR Spectra
TLDRThis video discusses a structure determination problem involving a chemical compound using various spectra including UV-Vis, IR, NMR, and mass spectrometry. The presenter focuses on interpreting IR and NMR data to deduce the compound's structure, suggesting an ester with a conjugated carbonyl group and an isopropyl group. The mass spec is used to confirm the structure, and the DEPT experiment is discussed for carbon type identification.
Takeaways
- 🔍 The video is a requested tutorial focused on determining the structure of a chemical compound using various spectroscopic data.
- 🌈 The presenter acknowledges their limited knowledge of UV-Vis spectroscopy and decides to focus more on IR, NMR, and mass spectrometry.
- 🔬 In the IR spectrum, the presence of a carbonyl group (C=O) at around 1710 cm⁻¹ and an aromatic benzene ring (around 1600 cm⁻¹) are clearly identified.
- 🔊 The IR spectrum also shows signals for sp3 CH bonds below 3000 cm⁻¹ and sp2 CH bonds above 3000 cm⁻¹, indicating the hybridization states of carbon atoms.
- 🧪 The mass spectrometry data suggests the presence of two oxygen atoms in the compound, likely in the form of an ester, as alcohols and carboxylic acids are ruled out based on the absence of specific IR peaks.
- 📊 The NMR data is crucial for identifying specific functional groups and structural elements, such as an isopropyl group indicated by a large doublet and a CH2 group bonded to oxygen, which is deshielded and appears far downfield.
- 🔎 The presenter methodically builds the structure by considering the integration of NMR peaks and the chemical shifts, leading to the identification of a CH2-CH-isopropyl linkage.
- 📚 The proposed structure is checked against the mass spectrometry fragments, confirming the presence of a conjugated ester and a benzene ring, which align with the observed fragments at m/z 77, 105, and 122.
- 📈 The DEPT (Distortionless Enhancement by Polarization Transfer) NMR is used to confirm the types of carbon atoms present (CH3, CH, CH2) and their arrangement in the molecule.
- 🏁 The final proposed structure is a plausible interpretation of all the spectroscopic data, integrating IR, NMR, and mass spectrometry results to form a coherent molecular structure.
Q & A
What is the main focus of the video?
-The main focus of the video is to determine the structure of a chemical compound using various spectra including UV-Vis, IR, NMR, and mass spectrometry.
Why does the presenter skip the UV-Vis spectrum analysis?
-The presenter skips the UV-Vis spectrum analysis because they find it less useful, possibly due to a lack of familiarity with interpreting UV-Vis data.
What is the first noticeable feature in the IR spectrum that the presenter identifies?
-The first noticeable feature in the IR spectrum is the carbonyl carbon-oxygen stretch at approximately 1710 cm-1, indicative of a ketone or aldehyde.
What does the presenter conclude about the presence of an aromatic benzene ring based on the IR spectrum?
-The presenter concludes that there is an aromatic benzene ring present, based on the peak at 1600 cm-1.
What does the presenter suggest about the presence of sp3 and sp2 hybridized CH bonds in the IR spectrum?
-The presenter suggests that there are sp3 hybridized CH bonds below 3000 cm-1 and sp2 hybridized CH bonds above 3000 cm-1.
Why does the presenter initially consider an ester in the structure of the compound?
-The presenter considers an ester because it can provide two oxygen atoms, which aligns with the presence of two oxygen atoms indicated by the mass spectrometry data.
What does the presenter identify as a key feature in the NMR spectrum that suggests an isopropyl group?
-The presenter identifies a large doublet in the NMR spectrum as a key feature suggesting an isopropyl group.
Why does the presenter think the CH2 group in the NMR spectrum is far downfield?
-The presenter thinks the CH2 group is far downfield because it is bonded to an electronegative oxygen, which pulls electron density away, shifting the signal downfield.
How does the presenter use mass spectrometry data to confirm the structure of the compound?
-The presenter uses mass spectrometry data to identify fragments that match the proposed structure, such as a benzene ring fragment and a rearranged fragment indicating a conjugated ester.
What role does the DEPT NMR play in confirming the structure of the compound?
-The DEPT NMR helps to confirm the presence of CH3, CH, and CH2 groups, providing further evidence for the proposed structure.
How does the presenter ensure that the proposed structure is consistent with all the given data?
-The presenter checks the proposed structure against the IR, NMR, and mass spectrometry data, ensuring that all observed features are accounted for and that the structure is chemically reasonable.
Outlines
🔍 Analyzing Spectra for Chemical Structure Determination
The speaker begins by acknowledging a video request from Australia and introduces the task of determining the structure of a chemical compound using various spectra, including UV-Vis, NMR, and mass spectrometry. They express a personal preference for ignoring UV-Vis data due to its perceived lack of utility, focusing instead on IR spectroscopy. The IR data reveals a carbonyl group at 1710 cm⁻¹ and an aromatic benzene ring at 1600 cm⁻¹. The speaker also notes the presence of sp3 and sp2 hybridized CH bonds. A minor peak around 3400 cm⁻¹ is observed but initially dismissed. The mass spectrometry data suggests the presence of an ester, given the chemical formula and the absence of alcohols or carboxylic acids.
🧩 Piecing Together the NMR Puzzle
The speaker dives into the NMR data, identifying a prominent doublet indicative of an isopropyl group, a CH linker, and a CH2 group bonded to an electronegative atom, likely oxygen. The integration of peaks and their positions in the spectrum help to deduce the presence of these groups. The aromatic region of the NMR is also discussed, with two distinct peaks suggesting symmetry. The speaker proposes a preliminary structure based on the NMR data, incorporating an ester, a benzene ring, and the identified groups. The structure is then cross-checked against the IR and NMR data to ensure consistency.
🔬 Confirming the Structure with Mass Spectrometry and DEPT
The speaker turns to mass spectrometry to confirm the proposed structure, identifying key fragments that correspond to the benzene ring and the ester group. A rearrangement is considered to explain a fragment at 122, which involves protonation and cleavage. The DEPT (Distortionless Enhancement by Polarization Transfer) NMR is used to further analyze carbon types, confirming the presence of CH3, CH, and CH2 groups. The speaker assigns labels to the carbons and protons in the proposed structure based on the DEPT and proton NMR data. The final structure is presented as a plausible solution that aligns with all the spectroscopic data discussed.
Mindmap
Keywords
💡UV-Vis
💡IR (Infrared)
💡NMR (Nuclear Magnetic Resonance)
💡Mass Spec
💡Aromatic Benzene Ring
💡Carbonyl Group
💡Isopropyl Group
💡CH2 Group
💡Conjugation
💡Fragment
💡DEPT
Highlights
Introduction to a structure determination problem with UV-Vis, NMR, and mass spec data.
Initial dismissal of UV-Vis data due to lack of utility in the analysis.
Identification of a carbonyl carbon-oxygen stretch in the IR spectrum at 1710 cm⁻¹.
Observation of an aromatic benzene ring in the IR spectrum indicated by a peak at 1600 cm⁻¹.
Detection of sp3 CH bonds just below 3000 cm⁻¹ and sp2 CH bonds just above 3000 cm⁻¹ in the IR spectrum.
Preliminary focus on the IR spectrum to establish a foundational structure.
Use of mass spectrometry data to infer the presence of an ester group due to the presence of two oxygen atoms.
Initial NMR analysis highlighting a large doublet suggestive of an isopropyl group.
Integration of NMR peaks indicating a CH linker with a septet and a doublet.
Consideration of the chemical shift of a CH2 group at 4.41 ppm, suggesting its bonding to an electronegative group.
Proposal of a structure with a conjugated ester and a benzene ring based on IR and NMR data.
Mass spectrometry analysis confirming the presence of a conjugated ester through fragment analysis.
Use of DEPT NMR to differentiate between CH3, CH2, and CH groups.
Assignment of NMR peaks to specific carbon atoms in the proposed structure.
Final proposal of a chemical structure that fits all the spectroscopic data.
Emphasis on the iterative process of structure determination, adjusting the proposed structure based on spectroscopic evidence.
Encouragement for viewers to engage with the content through comments and video requests.
Transcripts
Browse More Related Video
15.6a Interpreting NMR Example 1 | Organic Chemistry
15.6e Structural Determination From All Spectra Example 5 | Organic Chemistry
15.6d Structural Determination From All Spectra Example 4 | Organic Chemistry
Interpreting IR (Infrared) Spectra
Organic Chemistry II - Solving a Structure Based on IR and NMR Spectra
NMR Spectroscopy
5.0 / 5 (0 votes)
Thanks for rating: