Isomers of Butane - Definition, Types, Structure with FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:57 PM IST

Isomerism-The molecules having the same number and same types of atoms have the same formula, but have different physical and chemical properties.

Types of isomerism in butane

Constitutional isomers (Based on connectivity)

These are the isomers having the same chemical formula but the atoms or groups of atoms differ in their connectivity.

There is a possibility that butane can have two different structures based on connectivity. There can be straight chain butane as well as branched chain butane. Both these structures of butane fulfill the valency of the carbon atom and thus form four bonds. There are 13 total numbers of covalent bonds in butane as well as isobutane.

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This Story also Contains

Types of isomerism in butane
Structural isomers of butane
Isomers of butene
Structural isomers of C4H10O
Isomers of butyne

The name isobutane came from the fact that it is a constitutional isomer of butane. The structural unit of the ‘iso’ group is the carbon atom bonded to hydrogen and two -CH₃ groups. This is also known as chain isomerism. These are the isomers which differ in skeletons of carbon atoms.

n butane structure

Figure 1) n butane structure

isobutane structure

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Conformational isomers (Based on rotation around sigma bond)

Different spatial arrangements of atoms in molecules can be obtained due to free rotation around sigma bonds. All these arrangements are known as conformations. Carbon-Carbon bond in butane is a sigma bond therefore; rotation around the carbon-carbon single bond is possible. This rotation around the C-C single bond can occur without causing any effect on the overlap of orbitals.

Large number of spatial arrangements is possible due to this rotation. However, this rotation is not totally free. An energy barrier of about 1-20 kJ mol-1 has to be crossed to overcome the torsional strain. This torsional strain arises due to the repulsive forces between electron pairs. Two types of conformations are possible-

Eclipsed conformation- In this conformation the groups around the sigma bond are directly behind those of the other. A conformation can either be fully eclipsed or partially eclipsed. According to the same difference, the energy of a conformation can increase or decrease.

Staggered Conformation- In this conformation the groups around the sigma bond are staggered with respect to each other. Staggered conformation is of two types, anti and gauche conformation.

Conformational isomers

Four conformations are possible for butane, namely anti conformation, Gauche or skew conformation, eclipsed conformation, and fully eclipsed conformation. When the rotation takes place about the C₂-C₃ bond, the conformation with the two methyl groups opposite to each other (or 180⁰ away from each other) is called anti conformation and is maximum staggered.

Anti conformation of butane

Figure 3) Anti conformation of butane

With a rotation around the C₂-C₃ at an angle of 60⁰, this conformation becomes eclipsed; further rotation about an angle of 60⁰ will give skew conformation.

eclipsed conformation of butane

Figure 4) eclipsed conformation of butane

gauche conformation of butane

Figure 5) gauche conformation of butane

This conformation can also be staggered, however the methyl groups will be comparatively closer. Hence, there will be repulsions between the electron pairs which will lead to an increase in the energy of gauche conformation by 3.8 kJ/mol. A fully Eclipsed conformation is the most unstable conformation because the methyl groups are closest to each other. This fully eclipsed conformation has the highest energy and 19 kJ/mol more energy than the anti-conformation.

fully eclipsed conformation of butane

Figure 6) fully eclipsed conformation of butane

Structural isomers of butane

There are two possible isomers of butane.

n butane or neo butane structure

Figure 7) n butane or neo butane structure

N butane formula: C₄H₁₀

isobutane structure

Figure 8) isobutane structure

Isobutane formula: C₄H₁₀

IUPAC name of isobutane is 2-methylpropane. That means 2 methylpropane structure formulas are the same as isobutane structural formulas.

Both isobutane and n butane are C₄H₁₀ isomers.

To understand isomerism better, let’s examine more compounds that show isomerism.

Isomers of butene

There are four possible isomers of butene.

Butene molecular formula: C₄H₈

Butene structural formula and C₄H₈ IUPAC name is discussed below:

but-1-ene structure

Figure 9) but-1-ene structure

Trans-2- butene structure

Figure 10) Trans-2- butene structure

cis-2- butene structure

Figure 11) cis-2- butene structure

isobutene structure

Figure 12) isobutene structure

Where, cis-2-butene and trans-2-butene are geometric isomers of 2 butene. Here, but-1-ene and but-2-ene (both cis and trans) are position isomers of butene. , but-1-ene and but-2-ene (both cis and trans) and isobutene structure are structural isomers of butene.

Understanding the isomerism in but-2-ene-

Butene structure has four carbon atoms in which two carbon atoms are connected through a double bond. Just like how conformational isomerism was possible due to free rotation around the carbon-carbon sigma bond. Another type of isomerism is possible as a result of restricted rotation around a carbon-carbon double bond called geometrical isomerism.

Related Topics link,

Structural isomers of C₄H₁₀O

The compound C₄H₁₀O can show seven types of isomers excluding optical isomers.

ALCOHOLS:

butan-1-ol

2-methylpropan-1-ol

Figure 18) 2-methylpropan-1-ol

butan-2-ol

Figure 19) butan-2-ol

2-methylpropan-2-ol

Figure 20) 2-methylpropan-2-ol

ETHERS:

1-methoxypropane

Figure 21) 1-methoxypropane

2-methoxypropane

Figure 22) 2-methoxypropane

ethoxyethane

Figure 23) ethoxyethane

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Isomers of butyne

There are 2 isomers of butyne. 1-butyne structural formula and 2-butyne structural formula is given as:

1-butyne

Figure 24) 1-butyne

2-butyne

Figure 25) 2-butyne

There are 35 isomers of nonane and 75 isomers of decane.

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NCERT Chemistry Notes:

Frequently Asked Questions (FAQs)

1. Which of the following are isomers? A) Ethane and ethane B) Ethane and propane C) Ethane and ethyne D) Butane and isobutane

D) butane and isobutane

2. Among the isomeric alkanes of molecular formula C5H12, identify the one that on photochemical chlorination yields: A) Four isomeric monochlorides B) Three isomeric monochlorides C) A single monochloride

A) The isomer is 2-methylbutane

B) The isomer is n-pentane

C) The isomer is neopentane

3. N butane and isobutane are example of which type of isomerism?

N butane and isobutane are chain isomers and show structural isomerism.

4. How many isomers of butane can exist?

Two isomers of butane can exist

5. Isomers of a substance must have _.

Isomers of a substance must have the same molecular formula.

6. How many covalent bonds are present in butane?

7. What is isobutane?

isobutane is an isomer of butane.

8. Write name of chain isomers of butane.

n-butane and isobutane

9. 2-butyne and 1,3-butadiene are which isomers?

2-butyne and 1,3-butadiene are chain isomers.

10. Methylpropane is an isomer of?

Methylpropane is an isomer of n butane

11. What role do butane isomers play in the production of polymers?

Butane isomers, particularly isobutane, are important in polymer production. They can be converted to butenes, which are used to make various plastics and synthetic rubbers. Isobutane is also used in the production of high-octane gasoline components.

12. What is the significance of butane isomers in the study of conformational analysis?

Butane isomers, particularly n-butane, are important in the study of conformational analysis. The rotation around single bonds in n-butane leads to different conformations (e.g., anti, gauche), which is a fundamental concept in understanding the 3D structure and behavior of larger molecules.

13. What is the importance of butane isomers in the petroleum industry?

Butane isomers are significant in the petroleum industry as components of liquefied petroleum gas (LPG) and as feedstocks for producing high-octane gasoline components. They are also used in the production of various petrochemicals.

14. What is the significance of butane isomers in understanding molecular symmetry?

Butane isomers illustrate different molecular symmetries: n-butane has a higher symmetry (C2h point group) compared to isobutane (C3v point group). This difference in symmetry affects their spectroscopic properties and reactivity.

15. What is the importance of butane isomers in understanding the concept of isomer stability?

Butane isomers help illustrate the concept of isomer stability. Isobutane is slightly more stable than n-butane due to its more compact structure, which results in slightly stronger van der Waals forces between molecules.

16. What role do butane isomers play in the study of reaction mechanisms?

Butane isomers are useful in studying reaction mechanisms, particularly in free radical reactions. The different types of carbon atoms (primary, secondary, tertiary) in these isomers react at different rates, helping to elucidate the steps and selectivity of various reactions.

17. What is the significance of butane isomers in understanding the relationship between structure and thermodynamic properties?

Butane isomers clearly demonstrate how structural differences can lead to variations in thermodynamic properties such as heat capacity, entropy, and Gibbs free energy, despite having the same molecular formula. This relationship is fundamental to predicting the behavior of more complex chemical systems.

18. What role do butane isomers play in understanding the concept of molecular dynamics?

Butane isomers are useful models in molecular dynamics simulations. The different conformations of n-butane and the rigid structure of isobutane provide insights into molecular motion and energy landscapes in more complex systems.

19. How do the structures of butane isomers influence their behavior in polymer chemistry?

In polymer chemistry, the branched structure of isobutane can lead to the formation of polymers with different properties compared to those derived from n-butane. For example, polymers from isobutane derivatives may have lower melting points and densities.

20. What is the importance of butane isomers in understanding the concept of molecular orbital theory?

Butane isomers help illustrate how different structural arrangements can affect molecular orbitals. The branching in isobutane leads to slightly different orbital interactions compared to the linear n-butane, influencing their respective chemical properties.

21. How do butane isomers demonstrate the concept of structural diversity in organic chemistry?

Butane isomers demonstrate structural diversity by showing how the same number and type of atoms can be arranged in different ways to form distinct molecules. This concept is fundamental to understanding the vast number of possible organic compounds.

22. What role do butane isomers play in understanding the concept of steric hindrance?

Butane isomers help illustrate the concept of steric hindrance. The branched structure of isobutane creates more steric hindrance around its central carbon, affecting its reactivity in certain chemical reactions compared to the less hindered n-butane.

23. What is the significance of butane isomers in understanding the relationship between structure and physical properties?

Butane isomers clearly demonstrate how structural differences can lead to variations in physical properties such as boiling point, melting point, and vapor pressure, despite having the same molecular formula.

24. What role do butane isomers play in understanding the concept of molecular recognition?

Butane isomers help illustrate the importance of molecular shape in recognition processes. The different shapes of n-butane and isobutane can affect how they interact with other molecules or receptor sites, which is crucial in fields like drug design and catalysis.

25. What is the importance of butane isomers in the study of conformational energy?

N-butane, with its linear structure, is particularly important in studying conformational energy. The energy differences between its various conformations (e.g., anti, gauche) provide insights into the factors affecting molecular stability and flexibility.

26. What are isomers of butane?

Isomers of butane are different structural arrangements of the same chemical formula C4H10. These compounds have the same number and type of atoms but differ in how those atoms are connected, resulting in different physical and chemical properties.

27. How many isomers does butane have?

Butane has two isomers: n-butane (normal butane) and isobutane (2-methylpropane). These are the only possible structural arrangements for the molecular formula C4H10.

28. What is the difference between n-butane and isobutane?

N-butane has a straight chain of four carbon atoms, while isobutane has a branched structure with three carbon atoms in the main chain and one carbon branching off. This structural difference leads to variations in their properties and behavior.

29. Why are butane isomers considered structural isomers?

Butane isomers are structural isomers because they have the same molecular formula (C4H10) but different structural arrangements of their atoms. The carbon skeleton differs between n-butane and isobutane, making them distinct compounds.

30. How do the boiling points of n-butane and isobutane compare?

N-butane has a higher boiling point (-0.5°C) compared to isobutane (-11.7°C). This difference is due to the more compact structure of isobutane, which results in weaker intermolecular forces and easier vaporization.

31. What is the importance of understanding butane isomers in organic chemistry?

Understanding butane isomers is crucial in organic chemistry as it introduces the concept of structural isomerism. This concept is fundamental to understanding more complex organic molecules, their properties, and reactions, which is essential in fields like pharmaceuticals and materials science.

32. How do butane isomers illustrate the concept of constitutional isomerism?

Butane isomers perfectly illustrate constitutional isomerism, a type of structural isomerism. They have the same molecular formula (C4H10) but different bonding arrangements of atoms, resulting in distinct compounds with different properties.

33. Can butane isomers interconvert under normal conditions?

No, butane isomers cannot interconvert under normal conditions. The transformation of one isomer to another would require breaking and reforming carbon-carbon bonds, which needs significant energy input and typically occurs only under specific catalytic conditions.

34. What is the relationship between the structures of butane isomers and their vapor pressures?

Isobutane has a higher vapor pressure than n-butane due to its more compact, spherical shape. This shape results in weaker intermolecular forces, allowing isobutane molecules to escape into the gas phase more easily than the linear n-butane molecules.

35. What analytical techniques can be used to distinguish between butane isomers?

Butane isomers can be distinguished using techniques such as gas chromatography, mass spectrometry, and NMR spectroscopy. These methods can identify differences in molecular structure, fragmentation patterns, and chemical environments of atoms.

36. What is the significance of butane isomers in everyday life?

Butane isomers are commonly used as fuel in lighters and portable stoves. They are also important in the petrochemical industry as raw materials for producing various chemicals and plastics.

37. How do the combustion reactions of n-butane and isobutane differ?

Both n-butane and isobutane undergo complete combustion to produce carbon dioxide and water. However, isobutane may burn slightly more efficiently due to its branched structure, which can lead to better mixing with oxygen during combustion.

38. How do the structures of butane isomers affect their behavior in mass spectrometry?

In mass spectrometry, n-butane and isobutane produce different fragmentation patterns. Isobutane tends to form a more stable tertiary carbocation, resulting in a higher abundance of certain fragment ions compared to n-butane.

39. How do the structures of butane isomers influence their behavior in gas storage applications?

The compact structure of isobutane allows for slightly more efficient gas storage compared to n-butane. This property is relevant in applications like compressed natural gas (CNG) fuel systems, where maximizing storage capacity is crucial.

40. What is the IUPAC name for isobutane?

The IUPAC (International Union of Pure and Applied Chemistry) name for isobutane is 2-methylpropane. This name reflects its branched structure, with a methyl group attached to the second carbon of a propane chain.

41. How does the structure of butane isomers affect their octane ratings?

Isobutane has a higher octane rating than n-butane due to its branched structure. Branched hydrocarbons are more resistant to knocking in engines, making isobutane a better additive for improving gasoline quality.

42. How do the melting points of n-butane and isobutane compare?

N-butane has a higher melting point (-138.3°C) compared to isobutane (-159.6°C). This difference is due to the more efficient packing of n-butane molecules in the solid state, requiring more energy to break apart.

43. How do the densities of n-butane and isobutane compare?

N-butane has a slightly higher density (0.579 g/cm³ at 20°C) compared to isobutane (0.563 g/cm³ at 20°C). This difference is due to the more efficient packing of the straight-chain n-butane molecules compared to the branched isobutane molecules.

44. How do the chemical reactivity of n-butane and isobutane differ?

Isobutane is generally more reactive than n-butane due to its branched structure. The tertiary carbon in isobutane is more susceptible to certain reactions, such as free radical halogenation, compared to the primary and secondary carbons in n-butane.

45. How do the flame characteristics differ between n-butane and isobutane?

Isobutane tends to produce a hotter, more intense flame compared to n-butane due to its higher energy content per unit volume. This property makes isobutane preferable in some applications, such as portable cooking stoves.

46. How do the critical temperatures of n-butane and isobutane compare?

Isobutane has a lower critical temperature (134.7°C) compared to n-butane (152°C). This means that isobutane becomes impossible to liquefy by pressure alone at a lower temperature than n-butane, which is important in refrigeration applications.

47. How do the structures of butane isomers affect their solubility in water?

Both n-butane and isobutane have very low solubility in water due to their non-polar nature. However, isobutane is slightly less soluble than n-butane because its more compact structure reduces the surface area available for interaction with water molecules.

48. What is the relationship between the structures of butane isomers and their enthalpies of combustion?

The enthalpy of combustion for isobutane is slightly lower than that of n-butane. This is because the branched structure of isobutane is slightly more stable, requiring less energy to break its bonds during combustion.

49. How do the infrared (IR) spectra of n-butane and isobutane differ?

The IR spectra of n-butane and isobutane show distinct differences, particularly in the fingerprint region. Isobutane shows additional peaks due to its branched structure, while n-butane has a simpler spectrum reflecting its linear structure.

50. How do the structures of butane isomers influence their use as refrigerants?

Isobutane is more commonly used as a refrigerant than n-butane due to its lower boiling point and higher vapor pressure. These properties allow isobutane to more efficiently absorb heat and convert to gas in refrigeration systems.

51. How do the structures of butane isomers affect their behavior in gas chromatography?

In gas chromatography, n-butane typically has a longer retention time than isobutane. This is because n-butane interacts more strongly with most stationary phases due to its linear structure, while the compact shape of isobutane allows it to move through the column more quickly.

52. What is the significance of butane isomers in the study of molecular polarity?

Both butane isomers are non-polar molecules, but they illustrate how structural differences can affect the distribution of electron density. The more symmetrical structure of n-butane results in a more even distribution of electrons compared to the slightly asymmetric isobutane.

53. How do the structures of butane isomers influence their behavior in fractional distillation?

In fractional distillation, isobutane will separate at a lower temperature than n-butane due to its lower boiling point. This difference allows for the separation and purification of these isomers in petroleum refining processes.

54. How do the structures of butane isomers influence their behavior in adsorption processes?

The linear structure of n-butane generally allows for better adsorption onto surfaces compared to the more compact isobutane. This difference is important in processes like gas separation and purification using molecular sieves.

55. How do the structures of butane isomers affect their behavior in combustion engines?

Isobutane performs better in combustion engines due to its higher octane rating. Its branched structure makes it more resistant to premature ignition (knocking) compared to the straight-chain n-butane, resulting in more efficient combustion.

56. What is the significance of butane isomers in understanding the concept of hyperconjugation?

Isobutane demonstrates hyperconjugation more effectively than n-butane. The methyl groups in isobutane can donate electron density to the central carbon, stabilizing the molecule and affecting its reactivity.

57. How do the structures of butane isomers affect their behavior in cryogenic applications?

Isobutane is often preferred in cryogenic applications due to its lower boiling point. It can maintain a liquid state at lower temperatures compared to n-butane, making it more suitable for certain low-temperature cooling systems.

58. What role do butane isomers play in understanding the concept of bond angles?

Butane isomers illustrate how structural arrangement affects bond angles. The tetrahedral arrangement around the central carbon in isobutane results in different bond angles compared to the more linear arrangement in n-butane.

59. How do the structures of butane isomers influence their behavior in fuel cells?

The different structures of butane isomers can affect their performance in fuel cells. Isobutane may be more easily broken down due to its branched structure, potentially leading to more efficient energy production in certain types of fuel cells.

60. How do the structures of butane isomers affect their behavior in supercritical fluid applications?

The different critical points of n-butane and isobutane affect their behavior as supercritical fluids. Isobutane reaches its supercritical state at a lower temperature, which can be advantageous in certain extraction or reaction processes.