Hemiaminal

Key takeaways

Hemiaminal belongs to mathematics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Hemiaminal to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Hemiaminal from memory before moving on to harder problems.

Reference excerpt

In organic chemistry, a hemiaminal (also carbinolamine) is a functional group or type of chemical compound that has a hydroxyl group and an amine attached to the same carbon atom: −C(OH)(NR2)−. R can be hydrogen or an alkyl group. Hemiaminals are intermediates in imine formation from an amine and a carbonyl by alkylimino-de-oxo-bisubstitution. Hemiaminals can be viewed as a blend of aminals and geminal diol. They are a special case of amino alcohols.

Classification according to amine precursor Hemiaminals form from the reaction of an amine and a ketone or aldehyde. The hemiaminal is sometimes isolable, but often they spontaneously dehydrate to give imines.

Addition of ammonia

The adducts formed by the addition of ammonia to aldehydes have long been studied. Compounds containing both a primary amino group and a hydroxyl group bonded to the same carbon atom are rarely stable ("The hemiaminal [derived from primary amines] is, except in very special cases... not observed"), as they tend to dehydrate to form imines which polymerise to hexamethylenetetramine. A rare stable example is the adduct of ammonia and hexafluoroacetone, (CF3)2C(OH)NH2. The C-substituted derivatives are obtained by reaction of aldehydes and ammonia:

3 RCHO + 3 NH 3 ⟶ ( RCHNH ) 3 + 3 H 2 O {\displaystyle {\ce {3 RCHO + 3 NH3 -> (RCHNH)3 + 3 H2O}}}

Addition of primary amines N-substituted derivatives are somewhat stable. They are invoked but rarely observed as intermediates in the Mannich reaction. These N,N',N''-trisubstituted hexahydro-1,3,5-triazines arise from the condensation of the amine and formaldehyde as illustrated by the route to 1,3,5-trimethyl-1,3,5-triazacyclohexane:

3 CH 2 O + 3 H 2 NMe ⟶ ( CH 2 NMe ) 3 + 3 H 2 O {\displaystyle {\ce {3 CH2O + 3 H2NMe -> (CH2NMe)3 + 3 H2O}}}

Although adducts generated from primary amines or ammonia are usually unstable, the hemiaminals have been trapped in a cavity.

Addition of secondary amines: carbinolamines (hemiaminals) and bisaminomethanes One of the simplest reactions entails condensation of formaldehyde and dimethylamine. This reaction produces first the carbinolamine (a hemiaminal) and bis(dimethylamino)methane (Me = CH3):

Me 2 NH + CH 2 O ⟶ Me 2 NCH 2 OH {\displaystyle {\ce {Me2NH + CH2O -> Me2NCH2OH}}}

Me 2 NH + Me 2 NCH 2 OH ⟶ Me 2 NCH 2 NMe 2 + H 2 O {\displaystyle {\ce {Me2NH + Me2NCH2OH -> Me2NCH2NMe2 + H2O}}}

The reaction of formaldehyde with carbazole, which is weakly basic, proceed similarly:

Again, this carbinol converts readily to the methylene-linked bis(carbazole).

Hemiaminal ethers Hemiaminal ethers have the following structure: R‴-C(NR'2)(OR")-R⁗. The glycosylamines are examples of cyclic hemiaminal ethers.

Use in total synthesis Hemiaminal formation is a key step in an asymmetric total synthesis of saxitoxin:

In this reaction step the alkene group is first oxidized to an intermediate acyloin by action of osmium(III) chloride, oxone (sacrificial catalyst) and sodium carbonate (base).

Illustrations

Hemiaminal: Methanolamine, a simple hemiaminal — Methanolamine, a simple hemiaminal

Worked examples

Example 1 — a first encounter with Hemiaminal

Start with the simplest possible case. Write down what Hemiaminal claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In mathematics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Hemiaminal before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Hemiaminal ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Hemiaminal

In research: Hemiaminal appears in mathematics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Hemiaminal in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Hemiaminal is common in secondary-school and first-year university syllabi. It links to neighbouring topics Functional groups, so understanding it makes those chapters shorter.
In everyday life: Look for Hemiaminal outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Hemiaminal in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hemiaminal means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Hemiaminal out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hemiaminal in simple terms?

In organic chemistry, a hemiaminal (also carbinolamine) is a functional group or type of chemical compound that has a hydroxyl group and an amine attached to the same carbon atom: −C(OH)(NR2)−. R can be hydrogen or an alkyl group.

Why does Hemiaminal matter?

Because it connects several mathematics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Hemiaminal?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Hemiaminal.