Definition Structure Types and Examples of Alicyclic Compounds
Given the Alicyclic Compounds Definition odour colour chemistry, an alicyclic compound is defined as any of a large class of organic compounds in which either three or more atoms of the carbon element are linked together in a ring. The bonds between the pairs of adjacent atoms can all be of the type designated single bonds (involving the two electrons), or a few of them may be either double or triple bonds (with either four or six electrons, respectively).
About Alicyclic Compounds
The six-membered rings, where a system of alternating single and double bonds can be envisioned, however, belong to another important class (which are aromatic compounds) and distinguished from the alicyclic compounds by a characteristically various pattern of chemical reactivity. Such alicyclic compounds, where the ring has either three or four carbon atoms, are less stable compared to the compounds having larger rings due to the angles formed by adjacent covalent bonds are smaller compared to is necessary for maximum effectiveness.
In the larger rings, all the bond angles contain the preferred value (up to 109.5°); consequently, the atoms present in the ring do not lie in one plane. The same restrictions on the angles in both double and triple bonds affect the alicyclic compound’s stability containing such bonds.
Types of Cyclic Organic Compounds:
Alicyclic Compounds
An organic compound is the one where the carbon atoms are linked to form either one or more rings. Aromatic compounds are excluded due to their special properties. Generally, alicyclic compounds resemble analogous aliphatic compounds.
An example of an alicyclic compound is: Cyclohexane (C6H12) and so are many terpenes, like menthol.
Characteristics of Alicyclic Compounds
They can be saturated or unsaturated.
They do not have an aromatic character.
Three or more atoms of carbon are linked to each other in a ring.
The pairs of adjacent atoms can all have single bonds with two electrons, or double or triple bonds with four or six electrons.
Alicyclic compounds with the ring containing three or four carbon atoms are less stable than the compounds with larger rings.
In larger rings, all the angles of the bonds are around the preferred value of 109.5° and the atoms in the ring are not placed in one plane.
Aromatic Compounds
A compound that contains at least one aromatic ring is defined as Aromatic compounds. The aromatic ring is a highly stable planar ring of atoms with resonance structures that consist of both alternating double and single bonds, for example, benzene. Aromatic compounds are so-called due to their special and strong characteristic odours.
Examples of Aliphatic Compounds
Some of the examples of aliphatic compounds can be given as methane (CH4, which is the simplest aliphatic compound, LNG (Liquified Natural Gas), isotane, propane, and acetylene (flammable and explosive). Also, polyethylene can be used in plastic form, but do not breathe the fumes of burning polyethylene because it is very toxic.
A few of the aliphatic compounds are cyclic in nature, but they can form unstable rings. However, their rings are not as stable as similar aromatic compounds.
Also, there are aliphatic acids that react with any of the base compounds; some examples of aliphatic acids are given as propionic acid, acetic acid, and butyric acid. Acetic acid too can be dangerous and harmful in strong concentration.
Uses of Alicyclic Compounds
Here are some of the applications of alicyclic compounds:
Methane: It is used as fuel in Bunsen burners, automobiles, ovens and water heaters. It is also used in refined liquid form as rocket fuel. Its other uses are in the generation of electricity, as an antifreeze ingredient in industries, in fertilizers and sanitation products.
Liquefied Natural Gas: Cooking, heating, generating electricity, fueling vehicles and manufacturing products like fertilizers, paints and medicines.
Propane: It is used in home heating, cooling, hot water heaters, gas fireplaces, clothes drying, pool heaters, backup generators, as BBQ fuel, and in LPG cars and vehicles as fuel.
Acetylene: It is used in welding, industrial raw material, to produce solvents and alkenes in plastic production, in glass manufacturing, cutting, flame scarfing, brazing, metallurgical heating and hardening.
Acetic Acid: Acetic acid is a metabolic intermediate produced naturally inside body fluids and plant juices. It is used to make vinegar by fermentation and oxidation of natural carbohydrates and in preparing metal acetates for printing processes. Vinyl acetate is used in the production of plastics, cellulose acetate in making photographic films and textiles, and ethyl and butyl acetates as solvents in paints, resins, and lacquers.
Characteristics of Aromatic Compounds
Usually, a compound is said to be aromatic, or it has aromatic characteristics when there is a planar, fully conjugated ring having 4n+2 electrons in the conjugated system, where n is an integer.
Aromatic compounds are more special and are more stable than expected. For example, benzene vs. 1, 3, 5-hexatriene. They both contain six carbons and three double bonds, and both have all their double bonds conjugated. From these particular similarities, one might expect they have the same heat of hydrogenation, or they have the same absolute energy. However, what we find is that, significantly, benzene is more stable compared to its linear counterpart.
The other characteristic of aromatic compounds can be given as their absorption spectra. Conjugation lowers the energy that is necessary for electrons to jump from HOMO to LUMO. This process results in aromatic compounds by absorbing light in the UV spectra. Often, this characteristic is used to aid in calculating the reaction rates or identifying the unknowns.
Also, there are several nuances and cute things concerning the aromatic compounds, such as how reactions work with aromatic compounds through the nucleophilic or electrophilic substitution or how the potential for aromaticity affects acidity (think cyclopentadiene).
Aliphatic Hydrocarbons
Aliphatic hydrocarbon solvents can be described as organic compounds whose carbon atoms are linked in the open chains, either branched or straight, rather than having a benzene ring. These solvents do not contain a benzene ring, but they are mixtures of saturated, branched-chain (Iso-paraffin), long straight chain (normal-paraffin), or cyclic paraffin.
They can be produced by the crude oil distillation with a proper boiling point range fraction, and after that, they are treated to improve their odour and colour. Also, aliphatic hydrocarbon solvents are considered aliphatic compounds, and they contain hydrogen and carbon that are joined together in branched trains, straight chains, or non-aromatic rings.
The alicyclic hydrocarbons of the type of alkene, alkane, and alkyne series are given as the aliphatic compounds, same as the fatty acids and several other compounds; thus, aliphatic compounds are used as the opposite of aromatic compounds.
In addition to their use as diluents or solvents in thinners and paints, they can be widely used in degreasing, oil extraction, rubber manufacturing, and also as carriers for disinfectants and aerosols.
How are Aliphatic Hydrocarbons Extracted?
Aliphatic compounds can be extracted by the process of Pressurized Fluid Extraction (PFE). In this process, organic and aqueous solvents are used. Another method of extraction of aliphatic hydrocarbons includes water being converted to hot steam from solid and semi-solid samples.
FAQs on Alicyclic Compound in Organic Chemistry
1. What is an alicyclic compound in organic chemistry?
An alicyclic compound is a cyclic organic compound that contains carbon atoms arranged in a ring but does not have aromatic character. It combines features of aliphatic and cyclic compounds.
- The term comes from aliphatic + cyclic.
- The ring can be saturated or unsaturated.
- Example: cyclohexane (C6H12) is a common alicyclic compound.
- Unlike benzene, alicyclic compounds do not follow aromatic stability rules.
2. What is the difference between alicyclic and aromatic compounds?
The main difference is that alicyclic compounds are cyclic but non-aromatic, while aromatic compounds are cyclic and follow Huckel’s (4n + 2) π-electron rule.
- Alicyclic compounds: May be saturated or unsaturated; do not show aromatic stability (e.g., cyclohexane).
- Aromatic compounds: Planar, conjugated rings with (4n + 2) π electrons (e.g., benzene, C6H6).
- Aromatic compounds show extra thermodynamic stability due to delocalized π electrons.
3. What are examples of alicyclic compounds?
Common examples of alicyclic compounds include cycloalkanes and cycloalkenes such as cyclopropane, cyclobutane, cyclohexane, and cyclohexene.
- Cyclopropane (C3H6) – three-membered saturated ring.
- Cyclohexane (C6H12) – six-membered saturated ring.
- Cyclohexene (C6H10) – six-membered ring with one double bond.
4. What is the general formula of alicyclic compounds?
The general formula of saturated alicyclic compounds (cycloalkanes) is CnH2n.
- Compared to alkanes (CnH2n+2), cycloalkanes have two fewer hydrogen atoms due to ring formation.
- Example: For n = 6, cyclohexane = C6H12.
- For unsaturated alicyclic compounds (cycloalkenes), the formula becomes CnH2n-2 if one double bond is present.
5. Are cycloalkanes considered alicyclic compounds?
Yes, cycloalkanes are a major class of alicyclic compounds because they are saturated cyclic hydrocarbons without aromatic character.
- They contain only single C–C bonds.
- They follow the general formula CnH2n.
- Examples: cyclopentane (C5H10), cyclohexane (C6H12).
6. What are the types of alicyclic compounds?
Alicyclic compounds are mainly classified into saturated and unsaturated cyclic compounds.
- Saturated alicyclic compounds: Only single bonds (e.g., cyclohexane).
- Unsaturated alicyclic compounds: Contain one or more double or triple bonds (e.g., cyclohexene).
- They may also be monocyclic (one ring) or polycyclic (multiple fused rings).
7. How are alicyclic compounds named in IUPAC nomenclature?
Alicyclic compounds are named by adding the prefix “cyclo-” to the corresponding open-chain hydrocarbon name.
- Count the number of carbon atoms in the ring.
- Use the base name (methane, ethane, propane, etc.).
- Add cyclo- before the name (e.g., cyclo + hexane = cyclohexane).
- Number substituents to give the lowest possible locants.
8. What is ring strain in alicyclic compounds?
Ring strain is the extra instability in a cyclic compound caused by deviation from ideal bond angles and torsional strain.
- Small rings like cyclopropane have high angle strain (60° vs ideal 109.5°).
- Torsional strain arises from eclipsed bonds.
- Larger rings like cyclohexane (chair form) have minimal strain.
9. Are alicyclic compounds saturated or unsaturated?
Alicyclic compounds can be either saturated or unsaturated depending on the presence of multiple bonds in the ring.
- Saturated: Only single bonds (e.g., cyclopentane, C5H10).
- Unsaturated: One or more double bonds (e.g., cyclopentene, C5H8).
10. Why are alicyclic compounds important in chemistry?
Alicyclic compounds are important because they help explain ring structure, conformational analysis, and reactivity in organic chemistry.
- They are used to study ring strain and conformational isomerism (chair and boat forms of cyclohexane).
- Many natural products and pharmaceuticals contain alicyclic rings.
- They serve as intermediates in industrial organic synthesis.
