19 Facts On Isoleucine Structure And Characteristics

Isoleucine is an essential nonpolar and neutral α-amino acid having a molecular mass of 131.175 g/mol. Let us discuss about the isoleucine structure in detail.

Isoleucine structure contains an amino group in its α position which becomes protonated at biological conditions. The central atom is sp3 hybridized with a nonplanar structure. This aliphatic amino acid can be synthesized by a multistep procedure between the reaction of 2-bromobutane and diethyl malonate.

Let’s focus on the following topics on isoleucine like polarity, a number of isomers, solubility with proper explanations.

How to draw Isoleucine lewis structure?

Lewis structure shows the nonbonding electrons as electrons dot around respective atoms of the molecule. Lewis structure of any molecule can be drawn by following the below steps.

  1. Determining the valence electrons: The constituent atoms of isoleucine are carbon, hydrogen, nitrogen and oxygen. Carbon, nitrogen, oxygen, hydrogen contains four, five, six and one electrons in their valence shell respectively.
  2. Finding out the bonding electrons: Five carbon atoms form the main hydrocarbon chain and they attached with each other by single bonds. 2 and 3 numbered carbon atoms are attached with amino group (NH2) and methyl (CH3) group respectively. 1 no carbon is carboxylic acid carbon and it is bonded with one oxygen atom by double bond and another oxygen atom (OH) with single bond.
  3. Finding out the nonbonding electrons: Among all the constituent atoms, only nitrogen and oxygen carry nonbonding electrons. Nitrogen has two and oxygen has four nonbonding electrons.
isoleucine structure
Isoleucine Lewis Structure

Isoleucine Lewis Structure Shape

To know the shape of isoleucine, the hybridization of the central atom should be determined first as mentioned below.

The shape of isoleucine structure contains carbon atoms which are sp3hybridized and possess a tetrahedral geometry. 2 no carbon is attached with an amino group and 3 no carbon is attached with a methyl group.

If the central atoms have any lone pair, then each of the carbon atom cannot possesses tetrahedral geometry instead of having sp3hybridization. Amino group is showing as the upward bond and the methyl group (attached with 3 no carbon atom) is showing as the downward bond with respect to plane of paper.

Shape of isoleucine.
Image Credit: Wikimedia Commons.

Isoleucine Lewis Structure Formal Charge

Formal charge which is described below, is the individual charge carrying by the constituent atoms. Most stable lewis structure can be decided from the formal charge calculation.

Formula of the formal charge of isoleucine is = Total number of valance electrons – number of electrons remain as nonbonded – (number of electrons involved in bond formation/2)

  • Formal charge carrying by each of the carbon atom = 4 – 0 – (8/2) = 0
  • Formal charge of each of the two oxygen atoms = 6 – 4 – (4/2) = 0
  • Formal charge of each of the hydrogen atom = 1 – 0 – (2/2) = 0
  • Formal charge of the nitrogen = 5 – 2 – (6/2) = 0

Isoleucine Lewis Structure Angle

The bond angle which can be predicted from hybridization of central atom in absence of lone pair in central atom, let us figure out here.

The angle of Isoleucine structure contains six carbon atoms and all of them have sp3hybridization and each of the carbon atom has tetrahedral geometry with four different substituents. Therefore, the bond angle should be nearly equals to 109.50.

If carbon atom has any nonbonding electrons or lone pair, then the bond angle will be deviated from 109.50 (actual bond angle of any sp2 hybridized atom) due to presence of lone pair- lone pair, lone pair-bond pair and bond pair-bond pair repulsion.

Isoleucine Lewis Structure Octet Rule

 Octet rule is having the electron configuration in any atom’s valence shell like its nearest noble gas’s outer most shell according to the periodic table. Let us explore it in detail in the following stanzas.

In the octet rule of isoleucine lewis structure, it consists of carbon, nitrogen, oxygen and hydrogen as the participating atoms. All of them is group 2 element except hydrogen. So, the nearest noble gas of all of them is neon having electron configuration in its valence shell 2s2 2p6.

Carbon forms  four bonds with four substituent atoms or groups. After bonding with four groups, it gains four more electrons in its valence shell. Now, the total number of valence electron becomes eight, which matches with neon. Oxygen can bond any two other atoms or groups and after bond formation its valence shell get two more electrons.

Nitrogen can make bond with three other atoms and it also achieve noble gas like electron configuration and fill octet. Octet rule is not applied for hydrogen rather it obeys duplet (having two electrons in 1s orbital like helium).Thus, octet rule is obeyed in case of all the atoms as all of them also gain eight electrons in its valence shell.

 Isoleucine Lewis Structure Lone Pairs

Lone pairs are basically valence electrons which are not involved in bonding and shown as electron dots in lewis structure. Let us talk about this.

Formula of calculation of isoleucine lewis structure lone pairs is = Total number of valance electron – number of bonded electrons.

  • Nonbonding electrons of carbon atom = 4 – 4 = 0
  • Nonbonding electrons of hydrogen = 1 – 1 = 0
  • Nonbonding electrons of oxygen = 6 – 2 = 4
  • Nonbonding electrons of nitrogen = 5 – 3 = 2

Thus, total nonbonding electrons in isoleucine are = (2×4) + (2×1) = 10

Isoleucine valence electrons

Valence electrons are the electrons of outer most shell electrons. Because of the greater reactivity of these electrons, they participate in bonding with other atoms in a molecule. Let us explain it in detail.

The valence shell electron configuration of carbon, nitrogen and hydrogen are 2s2 2p2, 2s2 2p3 and 2s2 2p4respectively. Therefore, carbon, nitrogen and oxygen have four, five, and six valence electrons in their respective valence shell. Hydrogen is a group one element and and has only one electron.

Is isoleucine ionic or molecular?

Covalency in any compound is generated by the sharing of electrons but ionic compound is formed through the complete transferring of electrons which is mentioned below in detail.

Isoleucine is supposed to be a molecular or covalent compound because positive and negative charged ion can not be formed after the dissociation of isoleucine like any ionic compound.

Why and how isoleucine is molecular or covalent compound?

The bonds between the atoms in isoleucine are formed due to the mutual sharing of valence electrons of each of the bond forming atoms. Let us talk about this in brief.

Isoleucine is molecular because the electrons between the atoms are shared through the covalent bonds. Ionic bonds can only be formed if electrons are permanently transferred from less electronegative atom to more electronegative atom and attached by coloumbic force of attraction.

These are absent in isoleucine. Therefore, it can’t be an ionic compound, rather it is a covalent or molecular compound.

Is isoleucine aromatic?

A compound can be aromatic if it is sp2 hybridized with a planar and cyclic structure having (4n+2) pi electrons. Let us discuss this in detail.

Isoleucine is not an aromatic compound due to having a non planar acyclic structure and sp3 hybridization of central atom (carbon).

Why and how isoleucine is not an aromatic compound?

There are some characteristics or rule of aromaticity like planarity, sp2 hybridization, presence of (4n+2) pi electrons with a cyclic structure. Let us understand the point in detail.

Neither isoleucine is planar, nor cyclic. It has long hydrocarbon chain. It does not contain (4n+2) number of pi electrons and the carbon atoms are sp3 hybridized.

Is isoleucine zwitter ion?

Zwitter ion is defined as the presence of positively and negatively charged ions. Let us learn about it in detail.

Isoleucine is a zwitter ion due to presence of two oppositely charged (positive and negative) ions, NH3+ and COO ion.

Why isoleucine is a zwitter ion?

In most of the cases, amino acids can be present in zwitter ionic form. Isoleucine is also not an exception. It forms zwitter ion at pH =7.3. Let us explain more about the zwitter ion in detail.

Zwitter ion is an ion containing both the positive and negative ion in equal amount. Thus, the net electrical charge of any zwitter ion is always zero. This ion can be obtained by transferring one proton from COOH group to NH2 group.

How isoleucine is a zwitter ion?

In the following pathway zwitter ion of isoleucine is formed explained briefly in in the following stanza.

The hydrogen atom from COOH group is transferred to the NH2 group and make it NH3+ and COOH group is changed to COO.

Is isoleucine hydrophobic or hydrophilic?

Hydrophobicity is defined as the repulsion from water molecule whether hydrophilicity is the attraction towards water molecules. Let us have a discussion on it in detail.

Isoleucine is always going to be hydrophobic and not hydrophilic in nature due to having the repulsive tendency towards water molecule.

Why isoleucine is hydrophobic in nature?

Hydrophobicity is the tendency to avoid water molecule. The reason behind the hydrophobicity is discussed below.

Hydrophobic and hydrophilic nature depends upon the presence of hydrophobic alkyl and hydrophilic polar group. Depending upon the structure, isoleucine is hydrophobic in nature because the alkyl group is large and it can’t be soluble in water.

How isoleucine is hydrophobic in nature?

This can be explained below by the characteristics of alkyl group present in isoleucine structure.

This alkyl group cannot form any hydrogen bonds with polar solvent and thus it remains insoluble and shows hydrophobicity.

Is isoleucine ketogenic or glucogenic?

Precursor of glucose is formed glucogenic and ketone precursor is formed from ketogenic amino acid which are mentioned below in detail.

Isoleucine is glucogenic as well as a ketogenic amino acid as both the precursor of ketone and glucose is formed form isoleucine.

Why and how isoleucine is ketogenic as well as glucogenic amino acid?

Some of the amino acids can be glucogenic as well as ketogenic like isoleucine, phenylalanine, threonine, tryptophan and tyrosine. Let us figure out these two terms for isoleucine.

They can form both the glucose as well as ketone precursor. Glucogenic amino acids can be converted into glucose by the glucogenesis process and ketogenic amino acids are those which can be degraded directly into acetyl-CoA, precursor of ketone.

Is isoleucine acidic or basic?

Acidity and basicity of any amino acid depends upon the number of amino and carboxylic acid group. Depending upon the structure whether isoleucine is basic or acidic or neutral is described below.

As it contains equal number of COOH and NH2 group in its structure. Therefore, it is a neutral amino acid. Isoelectric pH of isoleucine is 7.3 (neutral pH).

Why and how isoleucine is neutral?

Neutral nature of any amino acid is observed due to the presence of equal number of amino and carboxylic acid group. Let us find out on how this is neutral.

Isoleucine is neutral because of having equal number of COOH and NH2 group. If number of amino groups is greater than number of COOH group, then the amino acid is considered as basic and if number of COOH group exceeds NH2 group, then the amino acid will be called as acidic amino acid.

Three amino acids are available like-

  1. Acidic amino acid
  2. Basic amino acid
  3. Neutral amino acid

Is isoleucine polar?

Polarity can be decided by the size of the alkyl group present in any molecule. Let us find out the reason isoleucine is polar or nonpolar.

Isoleucine is nonpolar and not soluble in water due to the presence of large bulky alkyl group.

Why and how isoleucine is nonpolar?

Alkyl group of isoleucine is the main reason why it is nonpolar and it is described below.

Isoleucine is nonpolar because it has a bulky alkyl group. Polarity of amino acid depends upon the size of the alkyl group because alkyl groups are generally hydrophobic in nature.

For the large bulky alkyl group, it cannot let the whole molecule to be soluble in water. Only polar compounds can be soluble in water due to having same nature (polar-polar).

Is isoleucine chiral?

Chirality can be determined from the structure as well as the presence of the substituent atoms or groups. Then we can comment on the chirality of isoleucine. Let us discuss on it.

Isoleucine is definitely a chiral compound having four different substituents with two chiral centers.

Why and how isoleucine is chiral?

A carbon atom can be chiral if the four substituent groups around it will be different. Let us explore why isoleucine is chiral.

Isoleucine is chiral because it contains four different substituent atoms around the central atom. In isoleucine, second carbon is chiral because it has four different atom or group, NH2, COOH, alkyl group, hydrogen around it.

Besides that, the third carbon is also chiral because it also contains four different groups around it.

Is isoleucine an essential amino acid?

The basic concept of essential amino acid is clarified below.

Isoleucine is definitely an essential amino acid as it is not possible to synthesis isoleucine in our body.

Why and how isoleucine is an essential amino acid?

Essential amino acids which are mentioned below, are defined as those which living body cannot synthesis and should be taken from outside through different food stuffs ,

There are nine essential amino acids and isoleucine is one of them. It is very much important for building up muscle tissue. The required amount of isoleucine for an adult living organism is 20 mg per day.

Is isoleucine a polymer?

Polymers are formed by the adding of same or different monomeric units. Let us discuss on the point is isoleucine a polymer or not.

At certain point of time isoleucine is not a polymer, it is present as monomer molecule.

Why and how isoleucine is not a polymer?

This describes about the isoleucine whether it is polymer or not which is clarified in detail.

It is present as monomer. Amino acids can be present as monomer. Large amount of amino acids form macromolecule protein through condensation process (elimination of water molecule).

Does isoleucine have isomers?

Isomers have same molecular formula but with different molecular arrangement. The following stanza tells about that whether isoleucine has any isomers or not.

Definitely there are four isomers are available for the structure of isoleucine due to having two chiral centers.

Why and how isoleucine have isomers?

Number of isomers depends how many number of chiral carbon atoms are present in the molecule. Let us explain it in detail.

Isoleucine contains four isomers because it has total two carbon atoms (2 and 3 numbered carbon). To determine the number of isomers the formula is used. Number of isomers = 2n [n = number of chiral carbon atom]. Therefore, the total number of isomers of isoleucine is 22 = 4.


From the above article it can be concluded that, isoleucine is an essential amino acid, which is hydrophobic and nonpolar in nature. It can be present in two isomers (d and l), which can rotate the plane polarized light.

Aditi Roy

Hi..I am Aditi Roy, I have completed my graduation from University of Calcutta and am pursuing M.Sc in Chemistry from Techno India University. My area of specialization is on Inorganic Chemistry.

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