15.6c Interpreting NMR Example 3 | Organic Chemistry
TLDRThe video script discusses the process of determining the structure of an organic compound using its hydrogen deficiency index and NMR spectra. The speaker begins by calculating the hydrogen deficiency index, which reveals no unsaturation, indicating the absence of double bonds or rings. The analysis then moves to the carbon spectrum, where three unique carbon environments are identified, suggesting symmetry or free rotation. The proton NMR spectrum, characterized by singlets, indicates two hydrogen environments, one of which is downfield due to its proximity to an electronegative atom, likely chlorine. The integration ratio of the hydrogens (6:2) confirms the total count. The speaker constructs the molecule by piecing together the fragments, accounting for all atoms, and concludes with a symmetrical structure where two methyl groups are attached to a central carbon with chlorines on either end.
Takeaways
- 🧮 **Hydrogen Deficiency Index Calculation**: The formula used to calculate the hydrogen deficiency index is (2 * number of carbons) + 2 - (number of hydrogens) - (number of halogens).
- ⚖️ **No Unsaturation Detected**: The calculation resulted in zero, indicating no presence of pi bonds, rings, or double bonds in the compound.
- 📊 **Carbon Spectrum Analysis**: Three unique carbon environments were identified despite four carbons present, suggesting symmetry or free rotation.
- 🧲 **Downfield Signals in Carbon NMR**: The signals in the alkane region are downfield, likely due to bonding with electronegative atoms such as chlorine.
- 🧬 **Proton NMR Findings**: The proton NMR showed two singlet signals, indicating a lack of adjacent hydrogens and confirming the structure.
- 🔍 **Chemical Shift in Proton NMR**: The second signal was further downfield, suggesting it is bonded to a carbon that is also bonded to an electronegative element like chlorine.
- 📉 **Integration Ratio in Proton NMR**: The ratio of the two hydrogen environments was six to two, which corresponds to the total number of hydrogens in the compound.
- 🔢 **Multiplicity of 3 in Alkane Region**: The analysis started with multiples of 3 for the alkane region, suggesting two methyl groups attached to the same carbon that can rotate freely.
- 🏗️ **Fragment Assembly**: Two fragments were identified, each with a single bond to make, and the remaining atoms were accounted for in the structure.
- 🔗 **Valence Electrons and Bonding**: Chlorine, with seven valence electrons, typically forms one bond, which was considered when assembling the molecular structure.
- 🔄 **Symmetry in the Final Structure**: The final molecular structure is symmetrical, allowing for the two remaining chlorine atoms to be placed equivalently.
- 🧩 **Puzzle Piece Attachment**: The final step involved attaching the remaining puzzle pieces to the central fragment, resulting in the complete molecular structure as depicted by the NMR spectra.
Q & A
What is the formula used to calculate the hydrogen deficiency index?
-The hydrogen deficiency index is calculated using the formula: (2 * number of carbons) + 2 - (number of hydrogens) - (number of halogens).
What does a hydrogen deficiency index of zero indicate about the compound?
-A hydrogen deficiency index of zero indicates that there are no degrees of unsaturation in the compound, meaning no pi bonds, no rings, and no double bonds are present.
How many unique carbon environments are suggested by the three signals in the carbon NMR spectrum?
-The presence of three signals in the carbon NMR spectrum suggests that there are three unique carbon environments in the compound.
What does it imply if the signals in the carbon NMR spectrum are in the alkane region but far downfield?
-If the signals are in the alkane region but far downfield, it implies that some of the carbons are bonded to electronegative atoms, such as the chlorines in the given structure.
What does the multiplicity of a signal in the proton NMR spectrum indicate?
-The multiplicity of a signal in the proton NMR spectrum indicates the number of hydrogen environments adjacent to the proton environment in question.
Why are the signals in the proton NMR spectrum described as singlets?
-The signals are described as singlets because there are no hydrogens attached to the adjacent carbons, indicating that each hydrogen environment is isolated.
What is the significance of the chemical shift in the proton NMR spectrum?
-The chemical shift in the proton NMR spectrum indicates the environment of the hydrogens. A shift further downfield suggests that the hydrogens are bonded to a carbon that is also bonded to an electronegative element.
How does the integration ratio in the proton NMR spectrum help in determining the structure of the molecule?
-The integration ratio provides the relative number of hydrogens in different environments, which helps to deduce the connectivity and arrangement of atoms within the molecule.
What is the significance of the symmetry in the structure derived from the NMR spectra?
-Symmetry in the structure suggests that certain parts of the molecule are identical, which can simplify the interpretation of the NMR spectra and the overall understanding of the molecule's shape.
How does the placement of chlorine atoms affect the NMR spectra?
-The placement of chlorine atoms, being electronegative, affects the chemical shifts of the carbons and protons to which they are bonded, often causing these signals to appear further downfield in the NMR spectra.
What is the final structure of the molecule based on the interpretation of the NMR spectra?
-The final structure is a symmetrical molecule with two methyl groups attached to a central carbon, which in turn is bonded to two chlorine atoms, with an additional CH2 group bonded to one of the chlorines.
Why is it important to account for every atom in the molecular formula when interpreting NMR spectra?
-Accounting for every atom in the molecular formula ensures that the entire structure of the molecule is considered, preventing the omission of any functional groups or atoms, which is crucial for accurately determining the molecular structure.
Outlines
🧪 Analyzing a Molecule's Structure Using NMR Spectroscopy
The paragraph discusses the process of determining a compound's structure using Nuclear Magnetic Resonance (NMR) spectroscopy. The speaker begins by calculating the hydrogen deficiency index, which in this case indicates no unsaturation, ruling out the presence of pi bonds, rings, or double bonds. The analysis continues with the examination of the carbon spectrum, revealing three unique carbon environments despite four carbons being present, suggesting symmetry or free rotation. The proton NMR spectrum is then described, with two hydrogen environments identified, both in the alkane region, with one being further downfield due to its bond with an electronegative element, inferred to be chlorine based on the molecular formula. The integration ratio of the protons is confirmed as six to two, matching the total hydrogen count. The speaker constructs the molecular structure piece by piece, considering the multiplicity of signals and the chemical shifts, ultimately deducing the arrangement of carbons, hydrogens, and chlorines to form a symmetrical molecule as depicted by the NMR spectra.
Mindmap
Keywords
💡Hydrogen Deficiency Index
💡Degrees of Unsaturation
💡Carbon Spectrum
💡Alkane Region
💡Proton NMR
💡Chemical Shift
💡Integration
💡Multiplicity
💡Free Rotation
💡Electronegative Atoms
💡Valence Electrons
Highlights
Calculation of the hydrogen deficiency index is essential for understanding the structure of the compound.
The hydrogen deficiency index is calculated using the formula (2 * number of carbons) + 2 - (number of hydrogens) - (number of halogens).
In this case, the index calculation reveals no unsaturation, indicating no double bonds, pi bonds, or rings.
The carbon spectrum shows three unique carbon environments despite four carbons being present, suggesting symmetry or free rotation.
Signals in the carbon spectrum are located in the alkane region, indicating potential bonding with electronegative atoms like chlorine.
Proton NMR displays two hydrogen environments, both in the alkane region, with one further downfield due to electronegative element bonding.
Both hydrogen environments are singlets, indicating no adjacent hydrogens and a lack of multiplicity.
Integration in the proton NMR shows a 6:2 hydrogen ratio, which matches the total number of hydrogens in the compound.
Starting with multiples of 3 in the alkane region helps to deduce the structure, suggesting two methyl groups attached to the same carbon.
The second fragment is a CH2 group bonded to a chlorine atom, as inferred from the singlet signal and lack of adjacent hydrogens.
Accounting for all atoms in the formula is crucial to ensure all pieces of the molecular puzzle are considered.
The presence of one chlorine in the formula suggests the need for another chlorine to complete the structure.
Chlorine atoms typically form one bond due to their 7 valence electrons, influencing the structure's connectivity.
The first puzzle piece, with more than one attachment point, must be in the middle of the structure.
The remaining two puzzle pieces, each with a single attachment point, are placed at the ends of the structure.
Symmetry in the final structure is observed, allowing for flexibility in the placement of the terminal groups.
The final molecular structure is deduced by piecing together the fragments based on NMR spectra data.
Transcripts
Browse More Related Video
15.6a Interpreting NMR Example 1 | Organic Chemistry
15.5a The Chemical Shift in C 13 and Proton NMR | Organic Chemistry
15.6e Structural Determination From All Spectra Example 5 | Organic Chemistry
15.6b Interpreting NMR Example 2 | Organic Chemistry
15.6d Structural Determination From All Spectra Example 4 | Organic Chemistry
12.02 Carbon-13 NMR Spectroscopy
5.0 / 5 (0 votes)
Thanks for rating: