What Makes Alicyclic Compounds Unique in Organic Chemistry?
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 Compounds: Types, Properties & Examples
1. What exactly is an alicyclic compound?
An alicyclic compound is a type of organic compound that is both aliphatic (non-aromatic) and cyclic (forms a ring). Think of it as a straight-chain hydrocarbon that has been bent around to join its ends. These compounds can contain one or more carbon rings, but they do not have the special electronic properties of aromatic compounds like benzene.
2. Can you give some common examples of alicyclic compounds?
Certainly. Some of the most common alicyclic compounds that students learn about are the simple cycloalkanes. These include:
- Cyclopropane (a 3-carbon ring)
- Cyclobutane (a 4-carbon ring)
- Cyclopentane (a 5-carbon ring)
- Cyclohexane (a 6-carbon ring)
Examples can also be unsaturated, like cyclohexene, which has a double bond in its ring.
3. What is the main difference between alicyclic and aromatic compounds?
The key difference is in their chemical stability and structure. Aromatic compounds, like benzene, have a unique ring of delocalised electrons that makes them exceptionally stable and causes them to react in specific ways. Alicyclic compounds lack this special aromatic character. Their chemical behaviour is very similar to their corresponding open-chain aliphatic compounds (alkanes and alkenes).
4. I thought all cyclic compounds were saturated. Are alicyclic compounds always saturated?
No, that's a common misconception. While many simple alicyclic compounds like cyclohexane are saturated (containing only single carbon-carbon bonds), they can also be unsaturated. This means an alicyclic compound can have one or more double or triple bonds within its carbon ring, such as in cyclohexene or cyclopentyne. The defining feature is being cyclic and non-aromatic, not whether it is saturated.
5. How are alicyclic compounds different from general aliphatic compounds?
The main difference is their structure. Aliphatic compounds refer to any organic compound with carbon atoms in open chains (straight or branched). Alicyclic compounds are a special subgroup of aliphatic compounds where the carbon atoms form a closed ring. So, while an alicyclic compound like cyclohexane is aliphatic in its properties, an open-chain compound like hexane is aliphatic but not alicyclic.
6. Why is cyclohexane considered more stable than cyclopropane?
The difference in stability comes down to ring strain. In cyclopropane, the C-C-C bond angles are forced into a 60° triangle, which is very far from the preferred 109.5° angle for carbon atoms. This creates high angle strain. In contrast, cyclohexane can adopt a stable, puckered 'chair' shape where the bond angles are almost exactly 109.5°, resulting in minimal strain and much higher stability.
7. Are alicyclic compounds important in the real world?
Yes, they are very important. Alicyclic ring structures are the foundation for many crucial biological molecules. For instance, steroids like cholesterol and hormones like testosterone contain alicyclic rings. Many terpenes, which give plants like pine and citrus fruits their distinct smells, are also based on alicyclic structures. They are fundamental building blocks in both nature and synthetic chemistry.
