Unveiling the intricate world of essential oils, we encounter over 20 distinct functional groups in organic chemistry. However, within constituents, there are eight primary essential oil functional groups that dominate. These functional groups include alcohols, aldehydes, alkenes, ketones, esters, ethers, phenols, and phenylpropenes. In this enlightening chapter, we delve into the atomic structure of each functional group, uncover their unique properties, potential applications, and provide examples of oils and constituents containing these functional groups.
It is vital to grasp that functional groups and carbon backbones are distinct features of aromatic compounds. Consequently, a molecule can simultaneously belong to multiple classifications, such as being both a monoterpene and an alcohol. Furthermore, molecules can exist as sesquiterpene alcohols, monoterpene aldehydes, sesquiterpene ketones, and so forth. Each combination of terpene and functional group represents its own exclusive class of molecules, adding to the remarkable diversity of essential oils.
While this article presents generalizations derived from chemistry to facilitate grouping and categorizing oils, it is crucial to acknowledge exceptions to these generalizations. For instance, while many alcohols offer notable health benefits when used internally, there are specific alcohols not recommended for internal consumption. By understanding the complexities of functional groups, we gain a deeper appreciation for the multifaceted nature of essential oils and their potential applications.
Essential Oil Functional Groups
Alcohol
This group comprises an oxygen atom attached to the carbon backbone on one end and a hydrogen atom on the other. Alcohol molecules typically bear names ending with the suffix “-ol.” Notable examples of monoterpene alcohols include menthol, terpinen-4-ol, citronellol, geraniol, and linalool. On the other hand, sesquiterpene alcohols encompass santalol, isovalencenol, khusimol, cedrol (also known as eudesmol), and patchoulol (also referred to as patchouli alcohol). However, there exists one exception to the naming convention—eucalyptol, which is actually an epoxide, a specific type of ether.
The constituents containing alcohol functional groups possess distinct properties that make them highly versatile in various applications. Aromatically, they emit relaxing scents, helping to alleviate feelings of anxiety. Topically, they exhibit repellant activity, possess cleansing properties, and contribute to youthful-looking skin. Internally, they support the circulatory system and have a calming effect on the nervous system.
When seeking essential oils rich in monoterpene alcohols, turn to Melaleuca, Geranium, Coriander, Basil, and Lavender. On the other hand, oils abundant in sesquiterpene alcohols include Sandalwood, Vetiver, Cedarwood, and Patchouli.
Aledehyde
Delving into the realm of essential oils, the aldehyde functional group emerges as a powerful entity. It features a carbon double bonded to an oxygen, with the same carbon atom bonded to both a hydrogen and another carbon in the molecule’s primary backbone. Aldehyde molecules generally bear names ending with the suffix “-al” or “-aldehyde.” Noteworthy examples of monoterpene aldehydes include geranial, neral, cinnamaldehyde, cuminal, and decenal. On the other hand, sesquiterpene aldehydes, although less prevalent, encompass santalal, farnesal, and valeranal.
Aldehyde-containing constituents showcase unique properties that make them invaluable in various applications. Aromatically, they possess calming, relaxing, and protective qualities. Topically, they may assist in reducing the appearance of blemishes, promote healthy-looking skin, support oral health and hygiene, and impart a warming sensation. Internally, they contribute to the well-being of the cardiovascular, digestive, immune, and nervous systems, with many essential oils rich in aldehydes also known to support a healthy metabolism.
For essential oils abundant in monoterpene aldehydes, consider exploring Cassia, Cinnamon, Melissa, Lemongrass, and Lime.
Alkene
Alkenes are characterized by the absence of other functional groups and the presence of at least one double bond between carbon atoms in their backbone. Typically, alkene molecules bear names ending with the suffix “-ene.” Notable examples of monoterpene alkenes include alpha-pinene, sabinene, limonene, and gamma-terpinene. Similarly, sesquiterpene alkenes encompass Germacrene D, beta-caryophyllene, zingiberene, and alpha-cedrene. They possess no other functional groups and feature at least one double bond between carbon atoms, with many of them boasting multiple double bonds.
Renowned for their antioxidant properties, monoterpene and sesquiterpene alkenes play a significant role. Their numerous double bonds and the presence of ring structures make them highly effective at accepting lone electrons from free radicals.
Alkene-containing constituents showcase an array of enticing aromas. Aromatically, they offer a multitude of unique and pleasant fragrances. Topically, they provide antioxidant benefits for the skin and tissues. Internally, they deliver antioxidant benefits for the internal organs and may also support the nervous, immune, digestive, reproductive, integumentary, and circulatory systems.
To experience the benefits of alkene-rich essential oils, consider exploring Frankincense, Douglas Fir, Blue Tansy, Lemon, and Wild Orange for those abundant in monoterpene alkenes. For sesquiterpene alkenes, Ylang Ylang, Black Pepper, Copaiba, Melissa, and Ginger are excellent choices.
Ester
Esters are formed through the reaction between an alcohol and an acid. They feature a central carbon atom double bonded to an oxygen atom, single bonded to the backbone, and single bonded to a second oxygen atom.
On the other side of this second oxygen, we find a short hydrocarbon chain. Typically, these chains consist of one, two, or three carbon atoms. Due to the presence of two carbon chains in an ester molecule, they typically bear two-word names, with the second word ending in the suffix “-ate.” Noteworthy examples of monoterpene esters found in essential oils include linalyl acetate, methylamyl angelate, benzyl acetate, bornyl acetate, neryl acetate, methyl thujate, and methyl salicylate. Sesquiterpene esters, while relatively rare, can also be found in essential oils.
Ester-containing constituents offer a range of enticing properties. Aromatically, they promote relaxation, soothing, and balancing effects. Topically, they rejuvenate the skin, soothe the tissues, and provide protection against specific environmental threats. The internal use of esters varies from case to case. Some esters can support the health of the cardiovascular, immune, nervous, and digestive systems, while others are not recommended for internal consumption.
To experience the benefits of ester-rich essential oils, explore Lavender, Roman Chamomile, Helichrysum, Arborvitae, and Wintergreen for those abundant in monoterpene esters.
Ether
Ethers consist of an oxygen atom bonded between two carbon atoms. To qualify as an ether, the flanking carbons must solely form bonds with other carbons (or hydrogen). Ethers can be found within the main carbon chain or in ring structures, appearing as if an oxygen atom has replaced a carbon atom in the backbone. They can also be situated in the peripheral regions of certain molecules. However, ethers are not very common among monoterpenes.
The most prevalent ether found in essential oils is eucalyptol, also known as 1,8-cineole, which belongs to the monoterpene ether category. Anisole is another well-known monoterpene ether. In contrast, sesquiterpenes are more likely to contain ether groups. Notable examples include curzerene and furanoeudsema-1,3-diene, both classified as sesquiterpene ethers.
Ether-containing constituents offer a range of enticing properties. Aromatically, they have a soothing effect on emotions and promote feelings of clear airways. Topically, they possess surface cleaning properties and contribute to improved skin appearance. The internal use of ethers varies from case to case. Some ethers provide antioxidant support and aid in maintaining a healthy immune system, while others are not recommended for internal consumption.
To explore the benefits of essential oils rich in monoterpene ethers, consider delving into Cardamom, Eucalyptus, Rosemary, Melaleuca, and Peppermint. For oils abundant in sesquiterpene ethers, Myrrh and Vetiver are excellent choices.
Ketone
Ketones are characterized by a carbon atom double bonded to an oxygen atom. The two carbons flanking this central carbon must only be bonded to carbon (or hydrogen) atoms. Ketone molecules typically bear names ending with the suffix “-one.” For example, we have the well-known ketones menthone and carvone. However, there is also a notable exception to this naming pattern, such as the renowned ketone camphor. Additionally, many sesquiterpenes feature ketones in their chemical structure. Some examples of sesquiterpene ketones include jatamansone, rotundone, mustakone, faurinone, davanone, and leptospermone.
Ketone-containing constituents offer a wide range of properties. Aromatically, some ketones can energize and uplift, while others provide stability and grounding. Certain ketones are known to support feelings of open airways. Topically, they exhibit repellant properties and may contribute to maintaining clean and healthy-looking skin. The internal use of ketones varies depending on the specific case. Most monoterpene ketones are beneficial for digestive, gastrointestinal, and nervous system function and health. However, sesquiterpene ketones are generally not recommended for internal consumption.
To harness the benefits of essential oils rich in monoterpene ketones, explore the aromatic treasures of Spearmint, Dill, Peppermint, Geranium, and Caraway. For oils abundant in sesquiterpene ketones, consider indulging in the enchanting aromas of Spikenard and Frankincense.
Phenols
Phenols represent a special subtype of alcohols, characterized by an alcohol group (consisting of an oxygen and a hydrogen atom) attached to a benzene ring.
The benzene ring, featuring six carbon atoms arranged in a captivating hexagonal pattern with precisely three double bonds within the ring, serves as the backbone for phenols. As phenols are alcohols, their names also bear the suffix “-ol.” Among the most prevalent monoterpene phenols, we have thymol, carvacrol, and eugenol, each offering unique aromatic profiles and potential benefits. On the other hand, sesquiterpene phenols are relatively uncommon in essential oils.
Phenol-containing constituents boast an array of properties. Aromatically, they provide an invigorating and captivating fragrance. Topically, they exhibit powerful cleansing properties, making them excellent for both skincare and surface-cleaning applications. Internally, phenols offer antioxidant properties and support the proper function of various bodily systems, including cardiovascular, circulatory, digestive, gastrointestinal, immune, nervous, and respiratory systems.
To embrace the potential of monoterpene phenols, indulge in the captivating aromas and benefits of Thyme, Oregano, Clove, Cinnamon Bark, and Basil essential oils.
Phenylpropenes
A phenylpropene group exhibits a distinct structure, featuring a carbon atom in a benzene ring bonded to a second carbon, which in turn forms a double bond with a third carbon. The third carbon is then single bonded to a fourth carbon at the end of the chain, creating a captivating arrangement.
While phenylpropenes are predominantly found in monoterpene compounds, they are not widely prevalent in most essential oils. However, two exceptional phenylpropenes that do grace the aromatic landscape are anethole and chavicol (also known as estragole).
Phenylpropene-containing constituents possess a range of intriguing properties. Aromatically, they emit an energizing and captivating fragrance that can invigorate the senses. Topically, they contribute to overall skin health and appearance, making them a valuable asset in skincare routines. Internally, phenylpropenes may offer support to the cardiovascular system and promote healthy blood flow, contributing to overall well-being.
To experience the allure of monoterpene phenylpropenes, explore the aromatic delights and potential benefits of Fennel, Myrtle, Anise, Star Anise, and Basil essential oils.
Some Final Thoughts
Functional groups are specific arrangements of atoms within organic molecules that determine their chemical properties and behavior. They play a crucial role in the classification and understanding of organic compounds. Understanding these functional groups helps in categorizing and classifying organic compounds, predicting their properties, and exploring their potential benefits in aromatherapy, skincare, and overall well-being.
