Ch. 13 - Alcohols and Carbonyl CompoundsWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins
Johnny Betancourt

LiAlHalso known as lithium aluminum hydride or LAH, is a strong reducing agent meaning it will create less bonds to oxygen (more bonds to hydrogen). Commonly seen is its use on carbonyls such as carboxylic acid, esters, and amides.

For now all you really need to know is that LiAlH4 is going to add H’s to many types of molecules.

For some of LiAlH4’s properties here is the full rundown. We will start by looking at the structure of LiAlH4, or lithium aluminum hydride.

                                                                                 LiAlH4 Structure LiAlHStructure 

For most reactions in Organic Chemistry you will not need to memorize this structure unless drawing a mechanism. You will also see that LiAlH4 is sometimes abbreviated as simply LAH. Therefore, feel free to use either in reactions.

What can LiAlH4 (LAH) do?

A better question is: What can’t LiAlH4 do?!

You will soon see that LiAlH4 can be used in a variety of reactions in Organic Chemistry. Some of the most common places you will see it are the following:

1. Reduce Aldehydes to 1˚ Alcohols 

                                                    Aldehyde ReductionAldehyde Reduction

(Notice that the carbon of the carbonyl contains an invisible H not drawn in) 

Yes, most commonly seen is the use of LiAlH4 to reduce an aldehyde to a primary (1˚) alcohol. This occurs through a nucleophilic addition of H (hydrogen) from our reducing agent, followed by a protonation step.

What this means is we take an H from LiAlHand add it to our carbonyl. We then have an oxygen with a negative charge that obtains an H in the last step. (More on the mechanism later)

2. Reduce Ketones to 2˚ Alcohols

This will occur the same as aldehydes except that we will obtain a 2˚ (secondary) alcohol due to the fact that ketones contain an R group instead of the H that aldehydes have.

3. Reduce Carboxylic Acids to 1˚ Alcohols 

LiAlH4 on Carboxylic AcidLiAlH4 on Carboxylic Acid

Here, we see lithium aluminum hydride + our acid workup reducing a carboxylic acid to a 1˚ alcohol. Note, this will require 2 successive reduction steps.

Just to make sure you are staying awake, here’s a little challenge for you.

We know that LAH will reduce the blue carboxylic acid, but will it reduce the red alkene? Hmm… I will let you guys think that one over for a bit until we get to the end. (Stay tuned!)

4. Reduce Esters to 1˚ Alcohols 

Ester to Alcohols via LiAlH4

Ester to Alcohols via LiAlH4

Now, we get into esters being reduced to alcohols. We will obtain 2 products for a non-cyclic ester:

- one being the alcohol that forms from the carbonyl which will be primary (1˚). 

- the other will be the alcohol that forms from the carboxylate portion, or simply the O + the 3 carbons labeled in red. This alcohol does not have to be primary.

If a cyclic ester is our starting material, we will yield a diol as seen below:

Diols via Reduction of Cyclic EstersDiols via Reduction of Cyclic Esters

5. Reduce Epoxides to Alcohols

LiAlH4 on EpoxidesLiAlHon Epoxides

For an epoxide, the situation changes slightly because there is no carbonyl group present. After forming the epoxide through Epoxidation it simply becomes an Epoxide Ring Opening through the base-catalyzed mechanism. 

Pop quiz: Can you draw in the expected product? Remember epoxides get reduced to alcohols in the presence of LiAlH4. 

6. Reduce Amides and Nitriles to Amines

The reactions below feature an amide using LiAlH4 to yield an amine, and a nitrile or cyanohydrin being reduced via lithium aluminum hydride to a primary (1˚) amine.

Click here to learn more about the reduction of amides via LiAlH4, as well as other reduction reactions to form amines.

Amines from Amides with LiAlH4Amines from Amides with LiAlH4

More on Cyanohydrins (Nitriles).

LiAlH4 on NitrilesLiAlHon Nitriles

7. Reduce Acid Chlorides to 1˚ Alcohols 


Acid Chloride with LiAlH4

The last situation I want you to be aware of involving LiAlH4  is its use to reduce acid chlorides to primary (1˚) alcohols. This will occur via an aldehyde intermediate similar to carboxylic acid and require a protonation step after the second reduction with LAH.

(*Note: There may be other less common reactions not listed)


Still confused? Check out Clutch’s videos on reduction here

Answer to pop quiz:

Product-of-Epoxide-with-LiAlH4Product of Epoxide with LiAlH4

About the Mechanism of LiAlH4:

The type of mechanism used will be that of Nucleophilic Addition. The main steps involved are:

1) Attack carbonyl carbon (E+) with your nucleophile (Nu-)

2) Form the tetrahedral intermediate

3) Protonate to from your alcohol

Here is an example of what the mechanism would look like if we used LiAlH4 to reduce a carboxylic acid to an alcohol, by first reducing it to an aldehyde.

LiAlH4 Mechanism IntroductionLiAlH4 Mechanism Introduction

See how far you can get with the above mechanism (Scroll to the end for answer)

VS. NaBH4:

NaBH4 or sodium borohydride is another reducing agent that is not as strong as LiAlH4 therefore we will use it for only aldehydes and ketones where 1 equivalent of hydrogen is added. It can also be used for reduction of acid chlorides seen above.

Quick note: You may also see a reagent by the name of DIBAL-H (Diisobutylaluminium hydride). If you see it this is the molecule you should think of:

DIBAL-H StructureDIBAL-H Structure

It is another reducing agent out there, kind of like LiAl(OtBu)3 (Lithium tri-tert-butoxy aluminum hydride).

  • DIBAL-H is commonly used for its reduction of Esters and Nitriles to Aldehydes.
  • LiAl(OtBu)3, which can be thought of as the bulky LiAlH4, we will utilize for its ability to reduce Acid Chlorides to Aldehydes.

Link to videos on each of the 3 situations mentioned above.

What LiAlH4 (LiAlH4) can’t do: 

One big area where LiAlH4 fails is when we want to stop at aldehydes because it is so strong. This is also the case with alkenes and alkynes since they are non-polar groups. LiAlH4 will also not reduce such groups as well.

Uniquely, NaBH4 is able to reduce one special type of double bond. Sodium borohydride or NaBH4, unlike lithium aluminum hydride (LiAlH4), can reduce conjugated carbonyl compounds.

Here’s an example:

NaBH4-vs-LiAlH4NaBH4 vs LiAlH4

If you would like a quick refresher on non-polar groups & polarity here are 2 links you can check out!

A Quick Derivative of LiAlH4:

LiAlH4-Derivative LiAlH4 Derivative 

Just in case you see D’s instead of H’s in LiAlH4 don’t be alarmed. Deuterium is a heavy isotope of hydrogen and can be treated in a similar fashion as seen above!  

Final Thoughts:

So remember, these reagents such as LiAlH4, NaBH4, DIBAL-H and Lithium tri-tert-butoxy aluminum hydride are all reducing agents, which means they will add H’s to a molecule. (There may be a few others not mentioned as well but these are the most common)

They will add H (hydrogen) via a Nucleophilic addition and primarily yield alcohols except in a few cases. 

In all reactions you can assume acid workup as your final step, however most cases involving these reagents will not require a mechanism.

In the case that you do need to know the mechanism for reduction, here it is!

Answer: (mechanism)

LiAlH4 MechanismLiAlH4 Mechanism

Johnny Betancourt

Johnny got his start tutoring Organic in 2006 when he was a Teaching Assistant. He graduated in Chemistry from FIU and finished up his UF Doctor of Pharmacy last year. He now enjoys helping thousands of students crush mechanisms, while moonlighting as a clinical pharmacist on weekends.