1. What do you mean by antiperiplanar?
Anti-periplanar or Antiperiplanar refers to the A-B-C-D bond angles of a molecule in organic chemistry. The molecule becomes asymmetric at the Neumann ridge, with antiparallel functional groups facing up and down 180 degrees apart. Hyperconjugation occurs when parallel orbitals collide and become entangled.Anti-periplanar is the same as Syn-periplanar or synperiplanar. In syn-periplanar conformers, A and D are on the same side of the bond plane, and the dihedral angles AB and C-D are between +30 and -30 degrees.
2. What is the The Pinacol rearrangement?
The methyl group appears to be antiplanar to the active alcohol function of the pinacol rearrangement. The rearrangement reaction takes its name from the conversion of pinacol to pinacolone.Pinnacles are chemicals with two hydroxyl groups, one on each adjacent carbon atom. It is a white solid organic matter.The pinacol rearrangement favors the synthesis of spirocyclic ketones when cyclic diol precursors are used. This type of rearrangement produces many spiro ring molecules. A chiral center is constructed near the heterocycle using a pinnacles rearrangement.
3. What is the Misuse, etymology and historiography of antiperiplanar?
Klein and Perilog first defined the term antiperiplanar in their 1960 paper "Explanation of Spatial Connections Across Single Bonds". Two functional groups on the opposite side of the bond face are called "anti". Periplanar is derived from the Greek word peri meaning "almost flat". According to Kane and Hersh, many organic textbooks use anti-peripheral plane to mean full-plane anti-plane or anti-coplanar, which is technically incorrect.
4. What do you mean by molecular orbital?
One of the key elements of antiperiplanar structure is the interaction between molecular orbitals. Antiperiplanar geometries place the bonding and antibonding orbitals nearly parallel or coplanar. 2-chloro-2,3-dimethylbutane shows the C-H σC-H bond orbital and the C-Cl σ*C-Cl anti-bond orbital, syn-periplanar. Parallel orbitals do overlapping . They also show their participation in hyperconjugation. If the bonding orbital is electron donating and the antibonding orbital is electron accepting, a bonding orbital can donate electronegativity to an antibonding orbital. This charged-to-uncharged acceptor-donor interaction has an overall stabilizing effect on the molecule. However, donating from a bonding orbital to an antibonding orbital also results in a weakening of both bonds. 2-chloro-2,3-dimethylbutane is stabilized by hyperconjugation via electron donation from σC–H to σ*C–Cl, but both the C–H and C–Cl bonds are weakened. Molecular orbital diagrams show that mixing σC-H and σ*C-Cl in 2-chloro-2,3-dimethylbutane lowers the energy of both orbitals.
5. What is the E2 mechanism?
A bimolecular elimination process occurs when the carbon-hydrogen bond is broken and the leaving group is placed in the anti-plane.For E2 to occur, the hydrogen and leaving group must be anti-planetary. Simply put, the hydrogen group and the leaving group must lie in the same plane, but in different directions, creating a "Z" configuration involving two carbons.
6. What does "antiperiplanar" mean in organic chemistry?
Antiperiplanar refers to a specific arrangement of atoms in a molecule where two groups or bonds are on opposite sides of a plane and parallel to each other. This configuration is crucial for certain reactions, particularly in elimination reactions like the E2 mechanism.
7. How does the antiperiplanar arrangement differ from synperiplanar?
In an antiperiplanar arrangement, the groups are on opposite sides of a plane and parallel, while in a synperiplanar arrangement, the groups are on the same side of the plane and parallel.
8. What is the dihedral angle in an antiperiplanar arrangement?
In an antiperiplanar arrangement, the dihedral angle between the two groups or bonds is 180°. This angle maximizes the distance between the groups and allows for optimal orbital alignment in reactions.
9. Can you explain the concept of "antiperiplanar" using the Newman projection?
In a Newman projection, an antiperiplanar arrangement is represented by two groups positioned 180° apart when viewed along a carbon-carbon bond. This projection clearly shows the optimal alignment for E2 elimination reactions.
10. Can antiperiplanar arrangements occur in cyclic compounds?
Yes, antiperiplanar arrangements can occur in cyclic compounds, but they are often more strained and less common than in acyclic molecules. The ring size and substituents can affect the ability of a cyclic compound to adopt an antiperiplanar conformation.
11. How does the antiperiplanar arrangement relate to the E2 mechanism?
In the E2 mechanism, the antiperiplanar arrangement is essential for the reaction to proceed. The leaving group and the proton being removed must be antiperiplanar to each other, allowing for the formation of the new π bond in the resulting alkene.
12. Why is the antiperiplanar arrangement important for E2 reactions?
The antiperiplanar arrangement maximizes orbital overlap between the breaking C-H and C-X bonds and the forming π bond. This alignment allows for the most efficient electron transfer and bond formation, making the reaction more favorable energetically.
13. How does the antiperiplanar arrangement affect the rate of E2 reactions?
The antiperiplanar arrangement significantly increases the rate of E2 reactions. This is because it provides the optimal geometry for orbital overlap, lowering the activation energy and making the reaction more favorable.
14. What is the relationship between antiperiplanar arrangement and stereochemistry in E2 reactions?
The antiperiplanar arrangement in E2 reactions leads to stereospecific elimination. The stereochemistry of the product alkene is determined by which hydrogen is antiperiplanar to the leaving group, resulting in predictable product formation.
15. How does temperature affect the likelihood of achieving an antiperiplanar arrangement?
Higher temperatures increase molecular motion and the probability of molecules adopting various conformations, including the antiperiplanar arrangement. This can lead to increased rates of E2 reactions at elevated temperatures.
16. Can you explain the etymology of "antiperiplanar"?
The term "antiperiplanar" is derived from three parts: "anti" (opposite), "peri" (around), and "planar" (relating to a plane). Together, they describe the arrangement of atoms or groups on opposite sides of and parallel to a reference plane.
17. Who introduced the concept of antiperiplanar arrangement in organic chemistry?
The concept of antiperiplanar arrangement was introduced by English chemist Derek Barton in the 1950s as part of his work on conformational analysis. This work significantly contributed to our understanding of reaction mechanisms and stereochemistry.
18. What are some common misconceptions about antiperiplanar arrangements in organic chemistry?
Common misconceptions include thinking that all elimination reactions require antiperiplanar arrangements (E1 doesn't), assuming it's always the most stable conformation (it's often higher energy), and overlooking its importance in reactions beyond E2 eliminations.
19. How does the antiperiplanar arrangement concept apply to the anomeric effect in carbohydrate chemistry?
The anomeric effect, which influences the stability of cyclic sugars, involves hyperconjugation between a lone pair and an antiperiplanar σ* orbital. This demonstrates how antiperiplanar relationships can affect molecular stability beyond just reaction mechanisms.
20. What is the significance of antiperiplanar arrangements in the design of enzyme inhibitors?
Understanding antiperiplanar arrangements is crucial in drug design, particularly for enzyme inhibitors. By designing molecules that can adopt antiperiplanar conformations similar to reaction transition states, chemists can create potent inhibitors that bind strongly to enzyme active sites.
21. Can you explain the difference between antiperiplanar elimination and synperiplanar elimination?
Antiperiplanar elimination occurs when the leaving group and the proton being removed are on opposite sides of a plane, while synperiplanar elimination occurs when they're on the same side. Antiperiplanar is generally more favorable due to better orbital overlap.
22. Can you describe the energy profile of a molecule rotating to achieve an antiperiplanar arrangement?
As a molecule rotates around a carbon-carbon bond to achieve an antiperiplanar arrangement, it goes through energy maxima (eclipsed conformations) and minima (staggered conformations). The antiperiplanar arrangement is often a local energy maximum but is crucial for certain reactions.
23. How does the concept of antiperiplanar arrangement apply to other reaction mechanisms besides E2?
While most prominent in E2 reactions, the antiperiplanar concept is also important in other stereospecific reactions, such as certain SN2 reactions, sigmatropic rearrangements, and some pericyclic reactions, where orbital alignment is crucial.
24. How does molecular strain affect the ability to achieve antiperiplanar arrangements?
Molecular strain can make it difficult for a molecule to adopt an antiperiplanar arrangement. In highly strained systems, such as small rings, the energy required to achieve this conformation may be prohibitively high, affecting reaction rates and outcomes.
25. What techniques can be used to experimentally determine if a reaction proceeds through an antiperiplanar transition state?
Experimental techniques include stereochemical analysis of products, kinetic isotope effects, and computational modeling. Additionally, spectroscopic methods like NMR can provide information about molecular conformations in solution.
26. How does the antiperiplanar concept apply to conformational analysis of complex molecules?
In conformational analysis, identifying potential antiperiplanar relationships between groups can help predict reactive conformations, especially for intramolecular reactions. This is crucial in understanding the reactivity and properties of complex organic molecules.
27. Can you describe how computational chemistry is used to study antiperiplanar arrangements?
Computational chemistry uses quantum mechanical calculations to model molecular geometries and energies. These methods can predict the likelihood of antiperiplanar arrangements, calculate energy barriers for conformational changes, and simulate reaction pathways involving these arrangements.
28. How does the presence of bulky substituents affect the likelihood of antiperiplanar arrangements?
Bulky substituents can hinder the adoption of antiperiplanar arrangements due to steric repulsion. This can lead to decreased reaction rates in E2 eliminations or favor alternative reaction pathways that don't require this specific geometry.
29. What is the relationship between antiperiplanar arrangements and hyperconjugation?
Antiperiplanar arrangements can facilitate hyperconjugation, a stabilizing interaction between filled and empty orbitals. This is particularly important in explaining the stability of certain conformations and the reactivity in elimination reactions.
30. How does the concept of antiperiplanar arrangement relate to the stereoelectronic effect?
The stereoelectronic effect, which describes how molecular orbitals influence reactivity and stability, is closely tied to antiperiplanar arrangements. The optimal orbital overlap in antiperiplanar conformations is a key example of stereoelectronic control in organic reactions.
31. How does solvent polarity affect the importance of antiperiplanar arrangements in E2 reactions?
Polar aprotic solvents tend to favor E2 reactions and enhance the importance of antiperiplanar arrangements. These solvents stabilize the charged transition state without interfering with the base, promoting the elimination reaction.
32. What role does antiperiplanar arrangement play in the regioselectivity of E2 reactions?
The antiperiplanar arrangement influences regioselectivity by favoring elimination of the most accessible antiperiplanar proton. This often leads to the formation of the more substituted alkene (Zaitsev's rule), but exceptions can occur based on steric factors.
33. How does the concept of antiperiplanar arrangement relate to the principle of least motion?
The principle of least motion suggests that reactions proceed through the pathway requiring the least atomic movement. The antiperiplanar arrangement aligns with this principle in E2 reactions, as it minimizes the motion required for elimination to occur.
34. What role does antiperiplanar arrangement play in the mechanism of E1cB reactions?
In E1cB (elimination unimolecular conjugate base) reactions, the initial step forms a carbanion intermediate. The subsequent elimination step often proceeds through an antiperiplanar arrangement between the leaving group and the developing π bond for optimal orbital overlap.
35. How does the concept of antiperiplanar arrangement apply to the analysis of reaction transition states?
In transition state analysis, identifying potential antiperiplanar relationships helps predict the most likely reaction pathway. The antiperiplanar arrangement often represents the lowest energy transition state for elimination reactions, guiding our understanding of reaction mechanisms.
36. Can you explain how antiperiplanar arrangements influence the stereochemistry of electrocyclic reactions?
In electrocyclic reactions, the concept of antiperiplanar arrangement helps explain the observed stereochemistry. The Woodward-Hoffmann rules, which predict the stereochemical outcome of these reactions, are based on the principle of maximum orbital overlap, often achieved through antiperiplanar alignments.
37. How does the antiperiplanar concept relate to the gauche effect in organic molecules?
The gauche effect, where certain molecules prefer a gauche conformation over an anti conformation, seems to contradict the preference for antiperiplanar arrangements. This apparent contradiction highlights the complex interplay of steric, electronic, and hyperconjugative effects in determining molecular conformations.
38. How does the concept of antiperiplanar arrangement apply to the analysis of reaction kinetics?
The requirement for antiperiplanar arrangement in certain reactions affects reaction kinetics. It can be a rate-determining factor, especially in conformationally restricted systems. Kinetic studies often consider the probability of achieving this arrangement when analyzing reaction rates and mechanisms.
39. Can you explain how antiperiplanar arrangements influence the reactivity of neighboring groups in organic molecules?
Antiperiplanar arrangements can facilitate neighboring group participation in reactions. For example, in certain substitution reactions, a neighboring group antiperiplanar to the leaving group can assist in the reaction, leading to stereospecific products and altered reaction rates.
40. How does the concept of antiperiplanar arrangement apply to the analysis of molecular orbitals in organic compounds?
In molecular orbital theory, antiperiplanar arrangements often allow for optimal overlap between orbitals involved in reactions. This concept is crucial in understanding bonding, antibonding, and non-bonding interactions, and in predicting reactivity based on orbital symmetry considerations.
41. What role does the antiperiplanar arrangement play in understanding the reactivity of conformationally locked systems?
In conformationally locked systems, such as certain bridged bicyclic compounds, the ability or inability to achieve antiperiplanar arrangements can dramatically affect reactivity. This concept is key in explaining the unique reactivity patterns observed in these rigid molecular structures.
42. How does the antiperiplanar concept relate to the principle of microscopic reversibility in chemical reactions?
The principle of microscopic reversibility states that the mechanism of a reverse reaction follows the same steps as the forward reaction, but in reverse order. The antiperiplanar arrangement, being crucial for many forward reactions, is equally important in understanding the reverse processes, maintaining consistency with this principle.
43. Can you explain how the concept of antiperiplanar arrangement is applied in the study of reaction dynamics?
In reaction dynamics, which examines the time-dependent behavior of reacting molecules, the antiperiplanar arrangement is often a key geometric parameter. Studying how molecules achieve and maintain this arrangement during a reaction provides insights into reaction pathways and energy landscapes.
44. How does the antiperiplanar concept influence our understanding of conformational isomerism?
The antiperiplanar concept is crucial in analyzing conformational isomers, particularly in acyclic systems. It helps explain the relative stability of different conformers and their reactivity, especially in cases where certain reactions are only possible from specific conformational states.
45. What is the relationship between antiperiplanar arrangements and the concept of stereospecificity in organic reactions?
Antiperiplanar arrangements often lead to stereospecific reactions, particularly in elimination processes. The requirement for this specific geometry ensures that the stereochemical information of the reactant is translated into predictable stereochemistry in the product, a key aspect of stereospecific reactions.
46. How does the concept of antiperiplanar arrangement apply to the analysis of reaction energy diagrams?
In reaction energy diagrams, the requirement for an antiperiplanar arrangement can appear as an energy barrier. The diagram may show an initial increase in energy as the molecule rotates to achieve this conformation, followed by a decrease as the reaction proceeds through the optimally aligned transition state.
47. Can you explain how antiperiplanar arrangements influence the regioselectivity of elimination reactions in complex molecules?
In complex molecules with multiple potential elimination sites, the ability to achieve antiperiplanar arrangements can dictate regioselectivity. The most accessible antiperiplanar hydrogen-leaving group pair often determines the major product, which may not always be the most substituted alkene.
48. How does the concept of antiperiplanar arrangement relate to the study of reaction mechanisms in organometallic chemistry?
In organometallic chemistry, antiperiplanar arrangements can be important in understanding ligand dissociation, reductive elimination, and certain types of insertion reactions. The concept helps explain the stereochemistry and rates of these processes in metal-mediated organic transformations.
49. What role does the antiperiplanar arrangement play in understanding the reactivity differences between cyclic and acyclic systems?
The ability to achieve antiperiplanar arrangements is often more constrained in cyclic systems compared to acyclic ones. This difference can explain reactivity variations, such as the generally slower elimination rates in small rings or the unique stereochemical outcomes in certain cyclic eliminations.
50. How does the antiperiplanar concept contribute to our understanding of asymmetric synthesis?
In asymmetric synthesis, controlling the geometry of reactive conformations is crucial. The antiperiplanar concept helps in designing chiral auxiliaries and catalysts that can enforce specific geometries, leading to stereoselective formations of new chiral centers.
51. Can you explain how the concept of antiperiplanar arrangement is applied in the field of total synthesis of natural products?
In total synthesis, understanding and exploiting antiperiplanar arrangements is crucial for planning key bond-forming or bond-breaking steps. It guides decisions on protecting group strategies, the order of reactions, and can be pivotal in achieving the desired stereochemistry in complex natural product targets.
52. How does the antiperiplanar concept relate to the principle of orbital symmetry conservation in pericyclic reactions?
The principle of orbital symmetry conservation, central to understanding pericyclic reactions, often involves analysis of orbital alignments similar to antiperiplanar arrangements. This concept helps explain why certain pericyclic reactions are thermally allowed while others require photochemical conditions.
53. What is the significance of antiperiplanar arrangements in understanding the mechanism of sigmatropic rearrangements?
In sigmatropic rearrangements, the antiperiplanar concept helps explain the observed stereochemistry and regioselectivity. The requirement for specific orbital alignments, often antiperiplanar, guides the migration of sigma bonds and determines the geometric outcome of these intramolecular rearrangements.
54. How does the concept of antiperiplanar arrangement contribute to the development of new synthetic methodologies in organic chemistry?
Understanding antiperiplanar arrangements has led to the development of new synthetic methods that exploit this geometry. This includes designing reagents that enforce antiperiplanar conformations, developing new elimination protocols, and creating stereospecific transformations based on this principle.
55. Can you explain how the antiperiplanar concept is applied in the study of enzymatic reactions in biochemistry?
In biochemistry, the antiperiplanar concept is crucial for understanding many enzymatic reactions, especially those involving eliminations or rearrangements. Enzymes often function by holding substrates in specific conformations, including antiperiplanar arrangements, to facilitate reactions. This concept helps explain enzyme specificity and the high efficiency of biochemical processes.
