TERBUTYL: STRUCTURE, CHARACTERISTICS, FORMATION, EXAMPLES - CHEMISTRY - 2025

The tertbutyl or tertbutyl is an alkyl group or substituent having the formula -C (CH ₃) ₃ and derived from isobutane. The prefix tert - comes from tertiary, because the central carbon atom, with which this group binds to a molecule, is tertiary (3rd); that is, it forms bonds with three other carbons.

Tert-butyl is perhaps the most important butyl group, above isobutyl, n-butyl, and sec-butyl. This fact is attributed to its bulky size, which increases the steric hindrances that affect the way in which a molecule participates in a chemical reaction.

Terbutyl group. Source: Pngbot via Wikipedia.

The upper image shows the tert-butyl group, linked to a side chain R. This chain can consist of a carbon and aliphatic skeleton (although it can also be aromatic, Ar), an organic functional group, or a heteroatom.

Terbutyl resembles fan blades or a three-toed foot. When it encompasses a large part of the structure of a molecule, as in the case of tert-butyl alcohol, the compound is said to be derived from it; and if, on the contrary, it is just a fraction or fragment of the molecule, then it is said to be nothing more than a substituent.

Nomenclature and training

Formation of terbutyl from isobutane. Source: Gabriel Bolívar via Mol View.

At first it was clarified what is the reason why this group is called terbutyl. However, this is the common name by which it is known.

Its name governed by the old systematic nomenclature, and currently also by the IUPAC nomenclature, is 1,1-dimethylethyl. To the right of the upper image we have the carbons listed, and it can be seen indeed that two methyls are bonded to carbon 1.

Terbutyl was also said to be derived from isobutane, which is the most branched and symmetric structural isomer of butane.

Starting from isobutane (left of the image), the central 3rd carbon must lose its only hydrogen atom (in red circle), breaking its CH bond so that the terbutyl radical, · C (CH ₃) _3, arises. When this radical manages to bind to a molecule or to a side chain R (or Ar), it becomes a substituent or tert-butyl group.

In this way, at least on paper, the compounds with the general formula RC (CH ₃) ₃ or Rt-Bu are obtained.

Structure and characteristics

The tert-butyl group is alkyl, which means that it is derived from an alkane, and that it consists only of CC and CH bonds. Consequently, it is hydrophobic and apolar. But these are not its most outstanding characteristics. It is a group that takes up too much space, it is bulky, and it is not surprising since it has three CH ₃ groups, large in themselves, linked to the same carbon.

Each CH ₃ of –C (CH ₃) ₃ rotates, vibrates, contributes to its molecular environment interactions by London dispersive forces. Not being enough with one, there are three CH ₃ that rotate as if they were the blades of a fan, the entire terbutyl group being remarkably bulky when compared to other substituents.

As a consequence, a constant steric hindrance appears; that is, a spatial difficulty for two molecules to meet and interact effectively. The terbutyl affects the mechanisms and how a chemical reaction proceeds, which will seek to take place in such a way that the steric hindrance is the least possible.

For example, atoms close to –C (CH ₃) ₃ will be less susceptible to substitution reactions; CH ₃ will prevent the molecule or group that wants to be incorporated into the molecule from approaching.

In addition to the aforementioned, terbutyl tends to cause a decrease in melting and boiling points, a reflection of weaker intermolecular interactions.

Examples of terbutyl

A series of examples of compounds where tert-butyl is present will be discussed below. These are obtained simply by varying the identities of R in the formula RC (CH ₃) ₃.

Halides

Replacing R with a halogen atom, we obtain the tertbutyl halides. Thus, we have their respective fluoride, chloride, bromide and iodide:

-FC (CH ₃) ₃

-ClC (CH ₃) ₃

-BrC (CH ₃) ₃

-IC (CH ₃) ₃

Of these, ClC (CH ₃) ₃ and BrC (CH ₃) ₃ are the best known, being organic solvents and precursors of other chlorinated and brominated organic compounds, respectively.

Tert-butyl alcohol

Tertiary butyl alcohol, (CH ₃) COH or t-BuOH, is another of the simplest examples derived from tert-butyl, which also consists of the simplest tertiary alcohol of all. Its boiling point is 82 ºC, being that of isobutyl alcohol 108 ºC. This shows how the presence of this large group negatively impacts intermolecular interactions.

Terbutyl hypochlorite

Substituting R for the hypochlorite, OCl ^- or ClO ^-, we have the compound terbutyl hypochlorite, (CH ₃) ₃ COCl, in which it stands out for its covalent C-OCl bond.

Terbutyl isocyanide

Structural formula of terbutyl isocyanide. Source: Edgar181 / Public domain

Now substituting R for the isocyanide, NC or -N≡C, we have the compound tert-butyl isocyanide, (CH ₃) ₃ CNC or (CH ₃) ₃ C-N≡C. In the image above we can see its structural formula. In it, terbutyl stands out to the naked eye like a fan or a three-fingered leg, and can be confused with isobutyl (with a Y shape).

Tertiary butyl acetate

Structural formula of tert-butyl acetate. Source: Edgar181 / Public domain

We also have the tert-butyl acetate, CH ₃ COOC (CH ₃) ₃ (upper image), which we obtain by substituting R for the acetate group. The terbutyl begins to lose structural priority because it is bound to an oxygenate group.

Diterbutileter

Structural formula of diterbutylether. Source: Wolfmankurd at English Wikipedia. / Public domain

The diterbutylether (upper image) can no longer be described with the formula RC (CH ₃) ₃, so the tert-butyl in this case behaves simply as a substituent. The formula of this compound is (CH ₃) ₃ COC (CH ₃) ₃.

Note that in their structure the two groups or terbutyl substituents resemble two legs, where the OC bonds are the legs of these; an oxygen with two three-toed legs.

So far the examples set forth have been liquid compounds. The last two will be solid.

Buprofezine

Structural formula of buprofezine. Source: Meodipt / Public domain

In the image above we have the structure of buprofezin, an insecticide, where on the far right we can see the "leg" of the terbutyl. At the bottom we also have the isopropyl group.

Avobenzone

Structural formula of avobenzone. Source: Fvasconcellos (talk • contribs) / Public domain

Finally we have avobenzone, an ingredient in sunscreen due to its high capacity to absorb UV radiation. The terbutyl, again, is located to the right of the structure due to its similarity to that of a leg.

Terbutyl is an all too common group in many organic and pharmaceutical compounds. Its presence alters the way in which the molecule interacts with its environment, since it is considerably bulky; and therefore, it repels in its path everything that is not aliphatic or apolar, such as the polar regions of biomolecules.

References

1. Morrison, RT and Boyd, R, N. (1987). Organic Chemistry. 5th Edition. Editorial Addison-Wesley Interamericana.
2. Carey F. (2008). Organic Chemistry. (Sixth edition). Mc Graw Hill.
3. Graham Solomons TW, Craig B. Fryhle. (2011). Organic Chemistry. (10th edition.). Wiley Plus.
4. Wikipedia. (2020). Butyl Group. Recovered from: en.wikipedia.org
5. Steven A. Hardinger. (2017). Illustrated Glossary of Organic Chemistry: Tert-butyl. Recovered from: chem.ucla.edu
6. James Ashenhurst. (2020). t-butyl. Recovered from: masterorganicchemistry.com