Conformation, Sawhorse and Newman Projections

Edited By Shivani Poonia | Updated on Jul 02, 2025 07:13 PM IST

Exactly assume that you are fitting a puzzle in the correct position according to the piece you have in your hand. You are turning, trying to adjust it to the best place with different angles; till it fits on each corner would be an obvious condition of molecules under different circumstances. For example, the use of the term conformation in organic Chemistry is to help people have an understanding of how molecules can take on shapes and geometry by merely rotating single bonds that do not cleave any bonds but facilitate the molecule's search through a vast conformational space of shapes and orientations.

This Story also Contains

Conformations
Types of Different Conformations and Aspects
Sawhorse Projections
Relevance and Applications
Some Solved Examples
Summary

Conformation , Sawhorse newman projections

Conformations

Conformation about a molecule may be a spatial arrangement of its atoms which will be brought about by rotation about a single bond. It does not depend on connectivity, as in the case of the definition of an isomer; they only depend on the different orientations of the same molecule. The molecule has many arrangements that can be acquired defining its chemical and physical properties. Listen, for example, the conformation of the drug molecule at the receptor site determines everything concerned about the efficacy of that drug at the receptor site.

Conformations

Alkanes contain carbon-carbon sigma (σ) bonds. Electron distribution of the sigma molecular orbital is symmetrical around the internuclear axis of the C–C bond which is not disturbed due to rotation about its axis. This permits free rotation about C–C single bond. This rotation results in different spatial arrangements of atoms in space which can change into one another. Such spatial arrangements of atoms that can be converted into one another by rotation around a C-C single bond are called conformations or conformers or rotamers. Alkanes can thus have an infinite number of conformations by rotation around C-C single bonds. However, it may be remembered that rotation around a C-C single bond is not completely free. It is hindered by a small energy barrier of 1-20 kJ mol^–1 due to weak repulsive interaction between the adjacent bonds. Such a type of repulsive interaction is called torsional strain.

Sawhorse projections

In this projection, the molecule is viewed along the molecular axis. It is then projected on paper by drawing the central C–C bond as a somewhat longer straight line. Upper end of the line is slightly tilted towards the right or left-hand side. The front carbon is shown at the lower end of the line, whereas the rear carbon is shown at the upper end. Each carbon has three lines attached to it corresponding to three hydrogen atoms. The lines are inclined at an angle of 120° to each other. Sawhorse projections of eclipsed and staggered conformations of ethane are shown in the figure.

NEET Highest Scoring Chapters & Topics

This ebook serves as a valuable study guide for NEET exams, specifically designed to assist students in light of recent changes and the removal of certain topics from the NEET exam.

Download EBook

Newman projections

In this projection, the molecule is viewed at the C–C bond head-on. The carbon atom nearer to the eye is represented by a point. Three hydrogen atoms attached to the front carbon atom are shown by three lines drawn at an angle of 120° to each other. The rear carbon atom is represented by a circle and the three hydrogen atoms are shown attached to it by the shorter lines drawn at an angle of 120° to each other. Newman’s projections for ethane are shown in the figure.

Sawhorse Projections

These projections are nothing but the representation of the three-dimensional conformation of the molecule into two dimensions. Key features of such a projection are: the view of a molecule is from an oblique manner, two neighboring carbons are shown and the spatial orientation of the groups about those two carbons are shown. The advantage of this method is that it gives a clear-cut view of the dihedral angles subtended by two substituents, and by that, it is of immense help in the process of the determination of the conformer stability, especially for the steric effects. Newman Projections The Newman projections are the second method to realize molecular conformations. This projection views along a carbon-carbon bond. In this view, we look down the viewer's line of sight at the substitutes which are attached to a pair of carbons. New man projections are particularly useful. They are in identifying and differentiating between properly staggered and eclipsed conformations of molecules. Generally more stable are the staggered conformations in which the substituents are now 60 apart, as greater separation of the atoms begins to become the point of minimum steric repulsion. In eclipsed conformations, the increase in higher energy is the result of an increase in steric strain, which derives from the overlapping of substituents.

Types of Different Conformations and Aspects

Different conformations mainly deal with staggered and eclipsed conformations. The staggered conformation is an arrangement in which the substituents of neighboring carbons are located as far from each other as possible with reduced energy, therefore maximizing stability. Two forms exist of a staggered conformation: gauche conformation and anti-conformation. The substituents in the gauche conformations are staggered 60° apart, while the substituents in the conformation are 180° apart. The radicals in the latter are the most twisted conformations because steric hindrance is the least there.

Sawhorse Projections

Dihedral angles can make the substituents differ to denote different conformations in the sawhorse projection. For example, in the staggered anti-conformation, the substituents need to be 180 degrees apart; in the gauche conformation, the substituents are 60 degrees apart. Chemists determine the most stable conformation of a molecule from sawhorse projections; this tells plenty about reactivity, stability, and interaction.

The use of Newman projections also allows a comparison of the staggered conformation with the eclipsed conformation. In a staggered conformation, the substituents of the front carbon are midway between the substituents of the rear carbon, hence reducing the effect of the repulsive forces, whereas, in an eclipsed conformation, there is the viewing of the substituents as well as its neighboring ones from the point of view of either substituent. This is held responsible for being associated with a higher energy of the conformation. This is exactly when the energy of several conformations can actually be observed by rotating Newman projections in the hope of observing which conformation is energy-favorable.

Relevance and Applications

Real-World Applications

Conformational analysis is a very important field, and the impacts that its consequences portray are huge for all fields, from pharmaceuticals to material science and biochemistry. For drug design, for instance, knowing the rightful preferred conformation of a given molecule will then be an easy task to predict motion toward the biological target. It is the adaptation of preferred conformational shapes for correct receptor fitting that makes beta-blockers more in their treatment of heart conditions in treatment.

Some Solved Examples

Example 1
Question:
Which one of the conformed of butane is the most stable?

1)Anti

2) Gauche

3) Eclipse

4) Fully Eclipse

Solution:

In anti, the two -−CH3CH₃remain farthest from each other, due to which it has the least bond

strain and has the highest stability,

Hence the correct option is (1)

Example 2
Question:
Staggered and eclipsed conformers of ethane are:

1) Polymers

2) (correct) Rotamers

3) Enantiomers

4) Mirror images

Solution:
Conformational isomers are called rotamers as they can be converted into each other by rotation about a single bond.

Hence, the correct answer is option (2).

Example 3
Question:
The dihedral angle in the staggered form of the Newman projection of 1,1,1-Trichloroethane is ......... degree. (Round off to the nearest integer)

1) (correct) 60

2) 45

3) 20

4) 90

Solution:
The staggered form of 1,1,1-Trichloroethane is given as:

The dihedral angle is 60 degrees.

Hence, the answer is 60.

Summary

In general, the structure or, better put, quality of the arrangement of atoms in a molecule is deduced by the conformation. There are Tucker's and other more advanced conformational analyses. Stability/ reactivity/prediction forms the tool of conformation analysis, which is exceptionally important both in the drug and material science field. These concepts' complexity allows chemists much information about molecular behavior and ways to design new compounds and materials with valued properties. So, this review identified some important features, elaborated on diversified varieties of conformations and their practical application, and, finally, gave a detailed guideline to this organic chemistry feature.

Frequently Asked Questions (FAQs)

1. What are conformations in organic chemistry?

Conformations are different spatial arrangements of atoms in a molecule that can be interconverted by rotation around single bonds. These arrangements result from the free rotation of sigma bonds and do not involve breaking or forming new bonds.

2. How do you determine whether a Newman projection represents the most stable conformation?

To determine if a Newman projection shows the most stable conformation: 1) Check if it's staggered (generally more stable than eclipsed). 2) Ensure large groups are as far apart as possible. 3) Look for any specific interactions (like hydrogen bonding) that might stabilize a particular arrangement. 4) Compare it with other possible conformations to confirm it has the lowest energy.

3. How do intramolecular hydrogen bonds affect conformational preferences?

Intramolecular hydrogen bonds can stabilize certain conformations that might otherwise be less favorable due to steric factors. They can cause molecules to prefer gauche conformations over anti conformations if the gauche arrangement allows for hydrogen bond formation.

4. What is the difference between a conformational isomer and a configurational isomer?

Conformational isomers are different spatial arrangements of the same molecule that can be interconverted by rotation around single bonds without breaking any bonds. Configurational isomers, on the other hand, cannot be interconverted without breaking and reforming bonds, and they often involve different arrangements around double bonds or chiral centers.

5. How does substitution affect conformational preferences in alkanes?

Larger substituents increase steric hindrance, potentially altering conformational preferences. Bulky groups tend to favor conformations that maximize their separation. Electronegative substituents may also influence preferences through electronic effects or intramolecular interactions.

6. What is the significance of studying conformations in organic chemistry?

Studying conformations is important because they can affect a molecule's reactivity, stability, and physical properties. Different conformations may have different energy levels, which can influence chemical reactions and biological activities of molecules.

7. How does torsional strain relate to conformational stability?

Conformations with higher torsional strain are less stable and have higher energy. Staggered conformations typically have lower torsional strain and are therefore more stable than eclipsed conformations, which have higher torsional strain due to closer proximity of groups.

8. What is the significance of anti and gauche conformations in alkanes?

Anti conformations have substituents on opposite sides of the carbon chain, maximizing their distance and minimizing steric interactions. Gauche conformations have substituents closer together, causing some steric hindrance. Anti conformations are generally more stable, but gauche can be favored in some cases due to other factors like intramolecular hydrogen bonding.

9. What is the relationship between conformational analysis and energy diagrams?

Conformational analysis often uses energy diagrams to show how the potential energy of a molecule changes as it rotates around a single bond. These diagrams typically show energy peaks for high-energy conformations (like eclipsed) and troughs for low-energy conformations (like staggered).

10. How do you determine the most stable conformation of a molecule?

To determine the most stable conformation: 1) Draw all possible conformations. 2) Identify steric interactions and other factors affecting stability. 3) Compare the relative energies of each conformation. 4) The conformation with the lowest energy is the most stable.

11. What is a sawhorse projection?

A sawhorse projection is a three-dimensional representation of a molecule that shows the spatial arrangement of atoms or groups around a carbon-carbon bond. It provides a perspective view of the molecule, showing bond angles and relative positions of substituents.

12. How does a sawhorse projection differ from a Newman projection?

While both represent molecular conformations, a sawhorse projection shows a 3D perspective view of the molecule, including bond angles. A Newman projection is a 2D representation viewed directly along a specific bond axis, focusing on the relative positions of groups attached to the two carbons of that bond.

13. How do you draw a Newman projection?

To draw a Newman projection: 1) Choose a carbon-carbon bond to view along. 2) Represent the front carbon as a point and the back carbon as a circle. 3) Draw the three groups attached to the front carbon extending from the point. 4) Draw the three groups attached to the back carbon extending from the circle.

14. What is the "gauche effect" and when does it occur?

The gauche effect is the unexpected preference for a gauche conformation over an anti conformation in certain molecules, particularly those with electronegative substituents. It occurs due to hyperconjugation or other electronic effects that stabilize the gauche conformation despite increased steric interactions.

15. What is meant by "conformational analysis" in organic chemistry?

Conformational analysis is the study of the different spatial arrangements (conformations) that a molecule can adopt due to rotation around single bonds. It involves examining how these conformations affect the molecule's properties, reactivity, and stability.

16. What is the difference between eclipsed and staggered conformations in a Newman projection?

In an eclipsed conformation, the groups on the front and back carbons align with each other when viewed along the bond axis. In a staggered conformation, the groups on the front carbon are positioned between the groups on the back carbon, maximizing the distance between them.

17. How do conformations differ from structural isomers?

Conformations are different spatial arrangements of the same molecule that can be interconverted by rotation around single bonds, while structural isomers have the same molecular formula but different bonding arrangements of atoms. Conformations do not involve breaking or forming new bonds, whereas structural isomers do.

18. Why are staggered conformations generally more stable than eclipsed conformations?

Staggered conformations are generally more stable because they minimize steric hindrance and electron-electron repulsion between groups on adjacent carbon atoms. This arrangement allows for maximum separation between atoms or groups, lowering the overall energy of the molecule.

19. What is torsional strain?

Torsional strain is the energy barrier that must be overcome to rotate around a single bond. It arises from the repulsion between electron clouds of groups on adjacent atoms as they pass close to each other during rotation.

20. What is a Newman projection?

A Newman projection is a two-dimensional representation of a molecule's conformation, viewed along a specific carbon-carbon bond. It shows the relative positions of atoms or groups attached to the two carbon atoms at either end of the bond being viewed.

21. What is the importance of conformational analysis in drug design?

Conformational analysis is crucial in drug design because a drug's biological activity often depends on its ability to adopt a specific conformation to interact with its target. Understanding conformational preferences helps predict how a drug molecule might bind to receptors or enzymes, influencing its efficacy and side effects.

22. How does temperature affect conformational equilibrium?

Higher temperatures provide more energy for molecules to overcome rotational barriers, leading to a more even distribution of conformations. At lower temperatures, molecules tend to favor the lowest energy conformations more strongly.

23. How do you determine the energy difference between two conformations?

The energy difference between conformations can be determined through: 1) Computational methods using molecular modeling software. 2) Experimental techniques like spectroscopy (NMR, IR) to observe population distributions. 3) Theoretical calculations based on known energy contributions from various interactions.

24. What is the "chair" conformation in cyclohexane, and why is it important?

The chair conformation is the most stable arrangement of cyclohexane, where the carbon atoms form a shape resembling a chair. It's important because it minimizes angle strain and torsional strain, making it significantly more stable than other conformations like the boat or twist-boat.

25. How do you convert between Newman and sawhorse projections?

To convert from Newman to sawhorse: 1) Draw the central bond at an angle. 2) Place front carbon groups on the lower end and back carbon groups on the upper end. 3) Adjust the angles to show 3D perspective. To convert from sawhorse to Newman: 1) Choose a viewing angle along the central bond. 2) Draw front carbon as a point, back as a circle. 3) Position groups around these points based on their relative positions in the sawhorse.

26. What is the concept of "rotational barrier" in conformational analysis?

The rotational barrier is the energy required to rotate around a single bond from one conformation to another. It represents the energy difference between the lowest and highest energy conformations during rotation. This barrier affects the ease of interconversion between different conformations.

27. How does electronegativity of substituents affect conformational preferences?

Highly electronegative substituents can influence conformational preferences through electronic effects. They may favor conformations that maximize orbital overlap (hyperconjugation) or allow for intramolecular interactions, sometimes leading to unexpected preferences like the gauche effect in certain molecules.

28. What is the significance of "syn" and "anti" terms in conformational analysis?

"Syn" refers to groups on adjacent carbons that are on the same side when viewed in a specific conformation, while "anti" refers to groups on opposite sides. These terms are important in discussing relative orientations of groups, particularly in cyclic compounds or in describing reaction mechanisms.

29. How do you determine the number of possible staggered and eclipsed conformations for a given molecule?

For a simple molecule with two different groups on each carbon: 1) There are three staggered conformations (rotation by 120° each). 2) There are three eclipsed conformations (rotation by 120° each). The total number can increase with more unique substituents, following the pattern of 3n staggered and 3n eclipsed conformations, where n is the number of unique arrangements.

30. What is the importance of conformational analysis in understanding reaction mechanisms?

Conformational analysis is crucial in understanding reaction mechanisms because: 1) Certain conformations may be required for reactions to occur (e.g., antiperiplanar arrangement in E2 eliminations). 2) The stability and accessibility of transition states depend on conformational factors. 3) Reaction rates and product distributions can be influenced by the conformations of reactants and intermediates.

31. How does ring strain affect the conformations of cyclic compounds?

Ring strain influences cyclic compound conformations by: 1) Limiting possible arrangements due to the constraints of the ring. 2) Causing some conformations to be higher in energy due to angle strain or torsional strain. 3) Sometimes leading to unexpected stable conformations that minimize overall strain (e.g., the envelope conformation in cyclopentane).

32. What is the "Karplus equation" and how is it used in conformational analysis?

The Karplus equation relates the dihedral angle between two hydrogen atoms to their coupling constant in NMR spectroscopy. It's used in conformational analysis to determine the predominant conformation of a molecule in solution by comparing observed coupling constants with those predicted for different conformations.

33. How do you use Newman projections to explain the relative stability of different conformations of butane?

Newman projections of butane show: 1) The anti conformation (methyl groups 180° apart) is most stable due to minimal steric hindrance. 2) Gauche conformations (methyl groups 60° apart) are less stable due to some steric interaction. 3) The eclipsed conformation with methyl groups aligned is least stable due to maximum steric hindrance.

34. What is the concept of "conformational equilibrium" and how does it relate to Boltzmann distribution?

Conformational equilibrium refers to the distribution of molecules among different conformations at a given temperature. The Boltzmann distribution describes this equilibrium, relating the energy difference between conformations to their relative populations. Higher energy conformations are less populated according to the equation: N₂/N₁ = e^(-ΔE/RT), where N₂ and N₁ are populations of two conformations, ΔE is their energy difference, R is the gas constant, and T is temperature.

35. How does hybridization affect conformational preferences?

Hybridization affects conformational preferences by influencing bond angles and electron distribution. For example: 1) sp³ hybridized carbons in alkanes prefer tetrahedral geometry, leading to staggered conformations. 2) sp² hybridized carbons in alkenes have restricted rotation due to the planar nature of the double bond. 3) sp hybridized carbons in alkynes have linear geometry, limiting conformational flexibility.

36. What is the "pentane effect" and how does it influence conformational stability?

The pentane effect refers to the destabilizing interaction between methyl groups in the gauche conformation of pentane and larger alkanes. It causes certain gauche conformations to be higher in energy than expected, influencing the overall conformational preferences of longer chain hydrocarbons.

37. How do you use sawhorse projections to analyze the conformations of cyclic compounds?

Sawhorse projections are useful for cyclic compounds because they: 1) Show the 3D arrangement of atoms in the ring. 2) Help visualize axial and equatorial positions in cyclohexane and similar rings. 3) Allow for easy comparison of different ring conformations, such as chair and boat forms in cyclohexane.

38. What is the significance of "pseudorotation" in cyclopentane conformations?

Pseudorotation in cyclopentane refers to the continuous interconversion between different envelope and twist conformations without passing through a planar state. It's significant because: 1) It allows cyclopentane to minimize overall ring strain. 2) It results in all carbons in cyclopentane being equivalent on the NMR time scale. 3) It demonstrates how flexible five-membered rings can be compared to six-membered rings.

39. How do intramolecular non-covalent interactions affect conformational preferences?

Intramolecular non-covalent interactions can significantly influence conformational preferences by: 1) Stabilizing certain conformations through hydrogen bonding or dipole-dipole interactions. 2) Causing some conformations to be favored despite apparent steric disadvantages. 3) Leading to folded structures in larger molecules like proteins and nucleic acids.

40. What is the concept of "conformational analysis" in the context of asymmetric synthesis?

In asymmetric synthesis, conformational analysis is crucial for: 1) Predicting the stereochemical outcome of reactions. 2) Designing chiral catalysts or reagents that can adopt specific conformations to induce stereoselectivity. 3) Understanding how substrate conformation influences the approach of reagents, affecting the stereochemistry of products.

41. How do you use Newman projections to analyze the conformations of substituted cyclohexanes?

Newman projections for substituted cyclohexanes: 1) View along each C-C bond to analyze interactions between substituents. 2) Compare axial vs. equatorial positions of substituents. 3) Identify 1,3-diaxial interactions that may destabilize certain conformations. 4) Determine the most stable chair conformation based on substituent preferences for equatorial positions.

42. What is the "A-value" and how is it used in conformational analysis?

The A-value is a measure of the energy difference between axial and equatorial positions for a substituent in cyclohexane. It's used to: 1) Predict the preferred conformation of substituted cyclohexanes. 2) Compare the steric bulk of different substituents. 3) Estimate the energy required for ring flipping in substituted cyclohexanes.

43. How do conformational changes affect the reactivity of functional groups?

Conformational changes can affect functional group reactivity by: 1) Altering the accessibility of the reactive site to reagents. 2) Changing the electronic environment of the functional group through different intramolecular interactions. 3) Influencing the stability of reaction intermediates or transition states. 4) Enabling or preventing intramolecular reactions depending on the proximity of reactive groups.

44. What is the importance of conformational analysis in understanding protein folding?

Conformational analysis is crucial in protein folding because: 1) It helps predict the most stable 3D structure of proteins based on amino acid sequences. 2) It explains how local conformational preferences (like α-helices and β-sheets) contribute to overall protein structure. 3) It aids in understanding how mutations or environmental changes can affect protein structure and function.

45. How do you use energy diagrams to represent conformational changes in molecules?

Energy diagrams for conformational changes typically show: 1) Energy levels of different conformations as troughs. 2) Energy barriers between conformations as peaks. 3) Rotation angle or reaction coordinate on the x-axis and potential energy on the y-axis. These diagrams help visualize the relative stability of conformations and the energy required for interconversion.

46. What is the concept of "conformational steering" in organic reactions?

Conformational