Organic Chemistry II - Solving a Structure Based on IR and NMR Spectra
TLDRIn this educational video, the instructor guides students through the process of deducing a plausible molecular structure based on given data, including a chemical formula (C11H14O2), IR and NMR spectra. They analyze key peaks to identify functional groups like esters, carbonyl bonds, and benzene rings, and piece together a structure consistent with the spectroscopic data.
Takeaways
- 🧪 The problem involves deducing the structure of a molecule given its chemical formula C11H14O2, along with IR and NMR spectroscopy data.
- 🔍 In the IR spectrum, peaks below 3000 cm⁻¹ indicate sp³ hybridized CH bonds, while those just above 3000 cm⁻¹ suggest sp² hybridized CH bonds.
- 📈 The peak at 1759 cm⁻¹ is identified as a C=O stretch, likely from an ester due to its position relative to typical ketones and acids.
- 🔑 The presence of a peak at 1600 cm⁻¹ is indicative of a benzene ring in the molecule's structure.
- 🔬 The NMR spectrum provides information about the hydrogen environment, with multiplets, singlets, and triplets indicating different chemical environments for the hydrogen atoms.
- 📊 A three-proton singlet at 2.3 ppm likely represents an isolated methyl group, possibly part of a phenol.
- 🔎 Two-proton doublets at 7.6 and 7.1 ppm suggest the presence of a symmetric phenyl ring in the molecule.
- 🧲 The NMR peaks at 0.9-1.0 ppm are indicative of methyl and methylene groups in an alkane chain, likely an ethyl or propyl group.
- 🔄 The structure deduced should be consistent with the given chemical formula, ensuring the correct number of carbon, hydrogen, and oxygen atoms are accounted for.
- 📝 The final step is to verify the proposed structure by checking that all NMR peaks are assigned to specific hydrogen atoms in a manner consistent with the spectroscopic data.
- 🏁 The overall goal is to propose a plausible molecular structure that is consistent with all provided data, including the chemical formula, IR, and NMR spectra.
Q & A
What is the molecular formula given in the script?
-The molecular formula given in the script is C11H14O2.
What type of bonds are indicated by the peaks just below 3000 in the IR spectrum?
-The peaks just below 3000 in the IR spectrum indicate sp3 hybridized CH bonds, suggesting the presence of alkane type bonds.
What does the peak at 3033 cm⁻¹ in the IR spectrum suggest?
-The peak at 3033 cm⁻¹ suggests the presence of sp2 hybridized CH bonds.
What type of functional group is indicated by the peak at 1759 cm⁻¹ in the IR spectrum?
-The peak at 1759 cm⁻¹ is indicative of a C=O double bond, likely a carbonyl group.
What type of carbonyl group is likely present based on the IR spectrum?
-Based on the IR spectrum, the carbonyl group is likely an ester, as the peak at 1759 cm⁻¹ is higher than typical for ketones or acids, and the presence of conjugation is ruled out.
What does the peak at 1600 cm⁻¹ in the IR spectrum suggest?
-The peak at 1600 cm⁻¹ suggests the presence of a benzene ring.
What is the significance of the 2.5 ppm peak in the NMR spectrum?
-The 2.5 ppm peak in the NMR spectrum is a two high triplet, indicating the presence of a methylene group (CH2) adjacent to a double bond or a ring.
What does the 2.3 ppm peak in the NMR spectrum indicate?
-The 2.3 ppm peak is a three high singlet, likely indicating an isolated methyl group (CH3), possibly part of a phenol.
What is the significance of the peaks at 7.69 ppm and 7.10 ppm in the NMR spectrum?
-The peaks at 7.69 ppm and 7.10 ppm in the NMR spectrum are indicative of aromatic protons, likely from a symmetric phenyl ring.
How does the presence of a propyl group affect the NMR spectrum?
-A propyl group would show up as a multiplet in the NMR spectrum due to the splitting of the methylene group (CH2) adjacent to the methyl group (CH3), resulting in a two high triplet and a three high triplet.
How does the script suggest verifying the proposed structure?
-The script suggests verifying the proposed structure by counting the hydrogen atoms in the structure to match the given molecular formula (C11H14O2) and ensuring that all the NMR and IR data are consistent with the proposed structure.
Outlines
🧪 Analyzing IR and NMR Spectra for Molecular Structure
The instructor begins by outlining the task of deducing a plausible molecular structure from given data, specifically the molecular formula C11H14O2 and spectroscopic data from IR and NMR spectra. The focus is on interpreting IR peaks to identify functional groups such as sp3 CH, sp2 CH, carbonyl (C=O), and aromatic rings. The IR spectrum suggests the presence of alkane-type sp3 CH bonds, sp2 CH bonds, a carbonyl group likely from an ester, and a phenyl ring. The strategy involves writing out all observed data and using this to propose a consistent molecular structure.
🔍 Interpreting NMR Data for Structural Elucidation
The second paragraph delves into the interpretation of NMR data, focusing on the chemical shifts and splitting patterns of protons. The instructor identifies key peaks such as a triplet at 2.5 ppm, a singlet at 2.3 ppm, and multiplets at 1.8 ppm and 1.0 ppm. These are associated with methyl groups, methylene groups, and ethyl groups, respectively. The presence of a symmetric phenyl ring is inferred from doublets at 7.69 and 7.1 ppm. The instructor proposes a structure incorporating an ester, a phenyl ring, and a propyl group, ensuring that the proposed structure is consistent with the observed NMR peaks.
📚 Verifying the Structure Against the Chemical Formula
In the final paragraph, the instructor emphasizes the importance of verifying the proposed structure against the given molecular formula, C11H14O2. By counting the carbon and hydrogen atoms in the proposed structure, the instructor confirms that it matches the formula, thus validating the structure. This step is crucial for ensuring that the molecular structure is not only consistent with the spectroscopic data but also with the elemental composition provided.
Mindmap
Keywords
💡IR Spectrum
💡NMR Spectrum
💡sp3 Hybridized CH Bonds
💡sp2 Hybridized CH Bonds
💡Carbonyl Stretch
💡Benzene Ring
💡Phenyl Ring
💡Ester
💡Methyl Group
💡Propyl Group
💡Chemical Formula
Highlights
Introduction to the problem of determining a plausible structure for a molecule given its formula and spectroscopy data.
Analysis of the IR spectrum to identify peaks corresponding to sp3 CH and sp2 CH bonds.
Identification of a C=O bond in the IR spectrum at 1759 cm-1, suggesting a possible ester group.
Discussion on the type of carbonyl stretch observed and its implications for the structure.
Use of the 1600 cm-1 peak to infer the presence of a benzene ring in the molecule.
Strategy for interpreting the NMR spectrum and labeling peaks for easier analysis.
Identification of a methyl group in the NMR spectrum at 2.3 ppm as a three high singlet.
Analysis of the NMR peaks at 1.8 ppm and 1.0 ppm to infer the presence of a methylene linker and a methyl group.
Discussion of the aromatic protons in the NMR spectrum, indicating a symmetric phenyl ring.
Hypothesis that the three high singlet at 2.3 ppm could be a phenol methyl group.
Proposed structure incorporating an ester, a ring, and a methyl group based on NMR data.
Analysis of the remaining NMR peaks to deduce the presence of a propyl group.
Final assembly of the proposed molecular structure based on all spectroscopy data.
Verification of the proposed structure against the given chemical formula C11H14O2.
Emphasis on the importance of labeling and interpreting spectroscopy data for accurate molecular structure determination.
Recommendation to double-check all proton assignments in the NMR spectrum to ensure consistency with the proposed structure.
Transcripts
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