Properties of Amides

Professor Dave Explains
6 Sept 201907:51
EducationalLearning
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TLDRIn this educational video, Professor Dave delves into the chemistry of amides, highlighting their unique properties and significance in nature. He explains the substantial energy barrier for rotation around the C-N bond due to partial pi bond character, supported by X-ray and IR spectroscopy data. The video also touches on the stability of amides, crucial for protein structure and function, and the prevalence of trans over cis isomers in secondary amides, foundational to peptide bonds in proteins.

Takeaways
  • 🧪 Amides are carbonyl-containing functional groups with a nitrogen atom bonded to two other groups, often found in nature and synthesized in labs.
  • 🔍 Dimethyl formamide (DMF) is a common polar, aprotic solvent that is miscible with water and frequently used in laboratories.
  • 🔁 The rotation around the C-N bond in amides is restricted due to the partial pi bond character between carbon and nitrogen, supported by zwitterionic resonance structures.
  • 📊 Empirical evidence from X-ray data shows amides are planar around the C=O region, similar to alkenes, indicating strong double bond character.
  • 🌡️ The carbonyl stretch in DMF occurs at a lower wavenumber than in ketones, suggesting delocalization of the carbonyl group in amides.
  • 🔮 NMR spectroscopy reveals a free energy barrier for rotation around the C-N bond in DMF, which is around twenty kilocalories per mole.
  • 🔬 Secondary amides can exist as E and Z isomers, with the trans isomer being significantly more stable due to steric reasons.
  • 🥚 Secondary amides are the structural basis of proteins, with peptide bonds formed during amino acid polymerization.
  • 🕊️ The stability of amides is crucial for the integrity of biomolecules in an aqueous environment, with a half-life of biological amides estimated at seven years.
  • 🧬 The presence of cis peptide bonds, although minimal in proteins, plays a role in protein structure and folding dynamics.
  • 🔬 The study of protein synthesis and organic synthesis of amides has seen significant advancements, with implications in both biochemistry and laboratory practices.
Q & A

  • What is an amide in the context of organic chemistry?

    -An amide is a functional group consisting of a carbonyl group adjacent to a nitrogen atom, with the nitrogen bonded to two other groups, which can be hydrogen or alkyl groups in various combinations.

  • What is the common prefix 'form' in the name of dimethyl formamide (DMF) signifying?

    -The prefix 'form' in DMF refers to the absence of alkyl groups on the other side of the carbonyl group, similar to the naming convention used in formaldehyde or formic acid.

  • Why is DMF a common solvent in the laboratory?

    -DMF is a common solvent due to its polar, aprotic nature and its miscibility with water, making it frequently used in various laboratory settings.

  • What is the energy barrier for rotation around the C-N bond in amides?

    -The energy barrier for rotation around the C-N bond in amides is substantial, due to the partial pi bond character between carbon and nitrogen resulting from the zwitterionic resonance structure of amides.

  • How does the resonance structure of amides affect the rotation around the C-N bond?

    -The resonance structure of amides, with the nitrogen's lone pair forming a pi bond to carbon, contributes to the composite structure, limiting the rotation around the C-N bond due to the presence of partial pi bond character.

  • What evidence supports the planarity of amides around the C=O region?

    -X-ray data provides strong empirical evidence for the planarity of amides around the C=O region, showing that amides are planar like alkenes, indicative of the strong double bond character.

  • How does the carbonyl stretch in an amide compare to that in a ketone?

    -The carbonyl stretch in an amide, such as DMF, appears at a lower wavenumber (around 1675) compared to a ketone (1700 or above), indicating that it takes less energy to stretch the carbonyl in an amide due to its delocalized nature.

  • What is the estimated free energy barrier for rotation around the C-N bond in DMF?

    -The estimated free energy barrier for rotation around the C-N bond in DMF is around twenty kilocalories per mole, which is typical for amides.

  • How can the stability of the trans isomer of secondary amides be explained?

    -The trans isomer of secondary amides is more stable due to steric reasons, similar to the stability of trans alkenes, and exists in much greater amounts (90 to 99 percent) compared to the cis isomer.

  • Why are secondary amides significant in biochemistry?

    -Secondary amides are significant in biochemistry because they form the basis of proteins. When amino acids polymerize, they form peptide bonds, which are secondary amides.

  • What is the estimated half-life of a typical biological amide?

    -The half-life of a typical biological amide has been estimated to be seven years, which is crucial for the stability of biomolecules in living organisms.

  • Why is the stability of amides important for protein metabolism?

    -The stability of amides is important for protein metabolism because it ensures that biomolecules do not fall apart too easily, yet allows for enzymes to promote hydrolysis of peptide bonds, enabling cells to obtain the necessary amino acids for building cellular machinery.

Outlines
00:00
🧪 Chemistry of Amides and Their Properties

Professor Dave introduces amides, a functional group with a carbonyl group adjacent to a nitrogen atom. Amides are characterized by the presence of two groups attached to the nitrogen, which can be hydrogen or alkyl groups. Dimethyl formamide (DMF) is highlighted as a common polar aprotic solvent that is miscible with water. The energy barrier for rotation around the C-N bond in amides is discussed, which is attributed to the zwitterionic resonance structure that partially delocalizes the pi bond between carbon and nitrogen. This is supported by X-ray data showing planarity similar to alkenes and IR spectroscopy indicating a lower energy carbonyl stretch compared to ketones. The free energy barrier for rotation in DMF is quantified using NMR data, demonstrating distinct signals for the methyl groups that coalesce upon heating, indicating rotation and chemical equivalence.

05:03
🥚 Amides in Biochemistry: Proteins and Stability

This section delves into the significance of secondary amides, which are foundational to proteins as they form peptide bonds during amino acid polymerization. It is noted that less than 0.1 percent of amino acid residues in proteins contain cis peptide bonds, which are less stable and less common due to steric hindrance, with the trans isomer predominating. The stability of amides is crucial for the integrity of biomolecules in an aqueous environment, with a half-life of biological amides estimated at seven years. This balance of stability is essential for both the structural integrity of proteins and their metabolism by enzymes. The discussion also hints at the importance of amide stability in the context of protein synthesis, both biologically and in the lab, and the impact on cellular machinery.

Mindmap
Keywords
💡Amide
An amide is a functional group that consists of a carbonyl group (C=O) bonded to a nitrogen atom, which is in turn bonded to two other groups, such as hydrogen or alkyl groups. Amides are central to the video's theme as they are the focus of the discussion on their synthesis, properties, and natural role. For instance, the script mentions that amides have a substantial energy barrier for rotation around the C-N bond due to their zwitterionic resonance structure.
💡Dimethyl Formamide (DMF)
Dimethyl formamide, or DMF, is a specific type of amide that has two methyl groups attached to the nitrogen atom. It is highlighted in the script as a common organic solvent, known for being polar, aprotic, and miscible with water. The script uses DMF as an example to discuss the unique properties of amides, such as the reduced energy required for carbonyl stretching compared to ketones.
💡Zwitterionic Resonance Structure
The zwitterionic resonance structure of amides refers to a particular way of drawing the bonding in which the nitrogen's lone pair forms a pi bond with the carbon, contributing to the stability and planarity of the molecule. This concept is crucial to understanding the restricted rotation around the C-N bond in amides, as illustrated by the script's discussion on the X-ray data showing amides to be planar.
💡Pi Bond
A pi bond is a type of chemical bond formed by the overlap of parallel p orbitals, resulting in a bond with two lobes of electron density. In the context of amides, the script mentions that there is partial pi bond character between the carbon and nitrogen due to the zwitterionic resonance, which influences the molecule's geometry and stability.
💡IR Spectroscopy
Infrared (IR) spectroscopy is an analytical technique used to identify functional groups in molecules by measuring the absorption of infrared light. The script refers to IR spectroscopy data to illustrate the difference in wavenumber between the carbonyl stretch in DMF and that in ketones, indicating the delocalization of the carbonyl group in amides.
💡Nuclear Magnetic Resonance (NMR) Spectroscopy
Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for determining molecular structures by analyzing the magnetic properties of certain atomic nuclei. The script uses NMR data to calculate the free energy barrier for rotation around the C-N bond in DMF, demonstrating how the technique can provide insights into the dynamics of molecular bonds.
💡Secondary Amides
Secondary amides are a type of amide where the nitrogen atom is bonded to one hydrogen and one alkyl group. The script discusses the existence of E and Z isomers in secondary amides, which are relevant to the structure of proteins, as peptide bonds in proteins are a form of secondary amides.
💡Cis and Trans Isomers
Cis and trans isomers refer to the spatial arrangement of groups around a double bond or a ring structure. In the context of secondary amides, the script explains that the trans isomer is more stable due to steric reasons, which is why it predominates in protein structures.
💡Peptide Bonds
Peptide bonds are the chemical bonds that link amino acids together in proteins, forming a polypeptide chain. The script mentions that peptide bonds are a type of secondary amide and discusses their stability, which is crucial for the integrity of proteins in biological systems.
💡Hydrolysis
Hydrolysis is a chemical process where a molecule of water breaks a bond in another molecule. The script highlights that amides are not particularly susceptible to hydrolysis, which is important for the stability of biomolecules in an aqueous environment like the human body.
💡Stability of Amides
The stability of amides is a key point in the script, as it discusses how the half-life of a typical biological amide is estimated to be seven years. This stability is essential for the functionality of proteins and the ability of enzymes to metabolize them, which is vital for cellular machinery.
Highlights

Introduction to amides as a carbonyl-containing functional group with a nitrogen atom bonded to two other groups.

Explanation of the simple amide, dimethyl formamide (DMF), its structure, and common uses as a polar aprotic solvent.

Discussion on the substantial energy barrier for rotation around the C-N bond in amides due to zwitterionic resonance structures.

Evidence from X-ray data supporting the planar structure of amides similar to alkenes, indicating strong double bond character.

Difference in geometry between amides and amines, with amides being planar due to resonance and amines being pyramidal.

IR spectroscopy data revealing lower energy required to stretch the carbonyl in an amide compared to a ketone, indicating delocalization.

Calculation of the free energy barrier for rotation around the C-N bond in DMF using NMR data.

Observation of distinct signals for methyl groups in DMF at room temperature, indicating a lack of rotation and chemical equivalence.

Demonstration of how warming the probe leads to the coalescence of signals in NMR, indicating increased rotation and chemical equivalence.

Introduction to secondary amides, their potential isomerism, and the use of E/Z or cis/trans nomenclature.

Stability preference of trans isomers in secondary amides due to steric reasons, similar to alkenes.

Relevance of secondary amides to protein structure, with peptide bonds being a form of secondary amide.

Statistic on the rarity of cis peptide bonds in proteins and their role in protein structure and folding.

Importance of amide stability in biological systems, with a half-life of biological amides estimated at seven years.

Discussion on the balance of amide stability for both integrity in biological systems and enzymatic hydrolysis.

Future discussion on protein synthesis in the context of laboratory organic synthesis.

Conclusion summarizing the enhanced understanding of amides and their properties.

Transcripts

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Related Tags
AmidesOrganic ChemistryDimethyl FormamideC-N BondResonance StructureProtein SynthesisBiochemistryIR SpectroscopyNMR DataPeptide Bonds