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Chemistry is essential to life on Earth and is intricately involved in the world around us. Though the word “chemical” generally denotes a negative connotation, chemicals are the building blocks of all that we experience. Chemistry may seem intimidating to many, but I hope that through these simplified concepts you will be able to expand your fundamental knowledge. 


Organic chemistry is the study of the chemical basis of all known life: the carbon atom. Other elements such as hydrogen, oxygen, nitrogen, and sulfur are also important in organic chemistry, but occur far less frequently than do carbon atoms.

All organic molecules have a hydrocarbon backbone in which a functional group composed of non-carbon atoms such as oxygen, nitrogen, or sulfur may reside. These groups increase hydrocarbon reactivity and impart a specific function. Included below is a diagram of the most common types of functional groups.

Carbon is most stable when it has formed four bonds with other atoms. The basic structure of all organic molecules is what is called a hydrocarbon chain. It includes a series of carbon atoms bonded together with all extra bonding spaces filled in by hydrogen. It can be a chain or a ring, branched or straight.

In chemistry, molecules are generally drawn using the symbols of the atoms (the symbol can be found on a Periodic Table) that are connected with straight lines. These lines represent the covalent chemical bonds that are formed between the atoms. One line indicates a single bond, two lines indicate a double bond, etc. Below is a chart showing the name and chemical structure for some simple molecules.

In organic chemistry, hydrocarbons are often drawn in simplified form with carbons represented by the corners or ends of lines with the lines themselves representing chemical bonds. Any atoms other than carbon and hydrogen are depicted by their proper chemical symbol. The chart of molecules below contains examples of hydrocarbons in simplified form.



Terpenes are the most commonly encountered class of hydrocarbons in essential oils. All terpenes are made up of a five-carbon molecule called an isoprene; thus, terpenes are classified by how many isoprenes they contain and have a total number of carbons that are a multiple of 5 (10, 15, 20 carbons, etc.). Terpene scientific names typically end in the suffix -ene.

Monoterpenes are some of the most ubiquitous terpenes in essential oils. They consist of two isoprenes bonded together to form a 10 carbon molecule and may be straight, branched, or cyclic. Common physical characteristics of monoterpenes are a low molecular weight, clear color, low viscosity, high volatility, and strong aroma. 

Because of their diversity, monoterpenes offer a wide array of health benefits, each oil will offer specific benefits. Many oils high in monoterpenes can:
  • Improve the appearance of skin blemishes
  • Support a healthy metabolism
  • Elevate mood

To the right is a table of common monoterpenes in essential oils and corresponding health benefits. 



Another common terpene is formed when an additional isoprene adds to a monoterpene to form a 15 carbon molecule called a sesquiterpene. With a higher molecular weight, sesquiterpenes are less volatile than monoterpenes, and are therefore less common in essential oils; however, they are important contributors to the synergistic functionality of essential oils.

Sesquiterpenes are often touted for their ability to promote calm, grounded feelings. Some sesquiterpenes can also aid in: 
  • Reducing the appearance of blemishes
  • Maintaining healthy circulation
  • Helping ease the stomach 
To the left is a table detailing sesquiterpenes commonly found in essential oils. 


The final class of terpene found in essential oils is the diterepene: the combination of two monoterpene units (a total of 20 carbons). Because of their high molecular weights, these molecules are difficult to extract by steam distillation, and when present (which is rare), they are found in essential oils in very low amounts. Diterpenes that may be found in essential oils include camphorene, cafestol, kahweol, cambrene, and taxideme.


The next layer of complexity in essential oil chemistry is the addition of functional groups to terpene backbones. Oxygenated groups are the most common type of functional group found in essential oils. As with terpenes, it is important to understand the different classes of oxygenated compounds that exist, as each class contributes its own unique potential health benefits.

Oxygenated essential oil constituents always have a terpene backbone, so the terpene name is still used in classifying the molecule. For instance, if an alcohol group (one oxygen and one hydrogen) was added to a monoterpene, the molecule would be called a monoterpene alcohol. In many cases however, the molecule is given a unique single name and the “monoterpene” or “ketone” words are omitted. 


Among the most widely studied and valuable functional groups found in essential oils are alcohols, which are groups composed of an oxygen and a hydrogen atom (usually written as “-OH”). A good way to identify these molecules is by looking at their scientific name, which often ends with the suffix “-ol.” Alcohols typically have pleasant aromas that are well tolerated.

Alcohols are a diverse class of compounds. Many alcohols:

  • beautify skin

  • promote calming relaxed feelings for a restful nights sleep. 


The next class of essential oil constituents are phenols, which have an alcohol group (OH) attached to a benzene ring. A benzene ring is a six sided carbon ring with three double bonds that result in electrons being “shared” between all of the carbon atoms. This effect gives rise to many beneficial properties including a powerful antioxidant benefit.

Phenols offer a myriad of powerful health benefits. Many help

  • Protect against seasonal threats 

  • Support healthy digestion

  • Support respiration


Phenols are very potent and can cause skin irritation, necessitating the dilution of essential oils high in phenolics. Below is a table showing essential oils high in phenolic compounds.


Aldehydes occur at the end of a carbon chain and include an oxygen with a double bond and a hydrogen (usually written C-H-O). This type of constituent can also be distinguished by looking at the scientific name, which usually ends with the suffix "-al" or "aldehyde" as a second word. Aldehydes are known for their distinctly potent fragrances and are often key contributors to the overall aroma of an essential oil.

Much of the aldehyde class offers

  • potent protection against environmental threats

  • some can help maintain healthy gastrointestinal function

  • some lessen feelings of stress


However, aldehydes can be irritating to those with sensitive skin, so dilution should be used as needed. Below are common aldehydes and the oils they’re found in.


Ketones are very similar to aldehydes as they also feature an oxygen with a double bond; however, this functional group always occurs somewhere in the middle of a carbon chain rather than on the end. Ketones can be identified from their scientific name, which usually end with the suffix “-one.”

Many ketones offer unique health benefits such as:

  • Relieving feelings of tension when applied topically 

  • Supporting healthy respiratory function

  • Exhibiting calming effects.


The following table shows the proportion and type of ketone constituents in a number of essential oils.


Esters are yet another essential oil functional group. An ester includes a carbon atom with a double bond to an oxygen molecule, a single bond to an oxygen molecule that has a single bond to another carbon molecule (usually written -COO- or -COOC-). Esters can be identified from the proper chemical name, which usually ends with the suffix “-yl, ” “-ate, ” or “-ester.”

Many esters are calming, relaxing and having balancing effects on mood.


Some can also be applied topically to reduce the appearance of blemishes and often give a soothing, warming sensation when applied topically to muscles.


Above are some common esters found in essential oils.


Oxides are the final class of essential oil functional groups and include an oxygen atom that is part of a hydrocarbon ring structure. Oxides can be distinguished based on their proper name which generally ends with the suffix “-oxide” or “-ole.”

Many oxides offer protection against environmental threats, support healthy respiratory function, and promote feelings of clear breathing.


When applied topically, some also rejuvenate and invigorate the skin.


Above is a table displaying common oxide constituents in essential oils. 


We have now reached the last part of the Essential Chemistry Series. If you have kept up with me this long then, great job! Now it's time to take all of that information we've learned and apply it into our daily lives. In these last few posts we will discuss a few simple application techniques.

When considering application methods for various oils, chemistry can be a key factor. For instance, when applied topically, oils high in monoterpenes will most easily penetrate the skin and be absorbed. Remember to take into consideration the chemical principles you’ve learned in this series to help you make your personal essential oil use more powerful.

A number of situations make substitution of essential oils necessary. Some essential oils should not be taken internally but by examining the chemical makeup of oils that can be used internally, it is easy to find a substitute. 

For instance, it is not appropriate to take White Fir internally; however, Frankincense, which can be taken internally, shares some chemical similarities with White Fir and while it cannot offer exact benefits it can be used as a close substitute.

Not all essential oils appeal to everyone. For instance, if Lavender does not appeal to you, but you seek calming benefits, Clary Sage, which is also high in linalyl acetate and promotes calming feelings, can be used instead. Substitutions can also be made out of convenience when particular oils are not on hand. An understanding of essential oil chemistry makes these substitutions intuitive and simple.


Now that you know the basics of chemistry, you can follow the chemistry wheel below. By knowing the backbones to an oil and it's compounds, you can see other oils that would work similar and give you results if one wasn't quite the right one. 

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