CHO- is the carbonyl functionality of organic chemistry, more specifically the aldehyde group. Let us discuss -CHO in detail in the following article.
The C in CHO- moiety is sp2 hybridized. CHO- is an aldehyde functionality having C=O, and for this reason, the carbon center is electrophilic. Because all the electron density from the carbon center is being dragged away towards the Oxygen site. So, -CHO is very much susceptible to nucleophilic attack.
CHO- is the specific group of carbonyl functionality. The aldehydes are more reactive due to the electronic and steric effects. There is only the H atom is attached to the double C-O, so there will be no chance of electron density dispersion, again due to the small size of H more bulky groups can attack here. Now we explore more about -CHO in the following section.
1. How to draw CHO- lewis structure?
Lewis structure can give us a clear idea about the shape, valence electrons, and bond angle of the CHO-. Now we see how to draw the CHO- lewis structure in a few steps.
Counting the valence electrons
The total valence electrons for the CHO- are 4+6+1+1 = 12. That is the summation of all individual atoms’ valence electrons that are present in the molecule. Valence electrons for C, O, and H are 4,6, and 1 as they are group IVA, VIA, and IA elements. One extra electron will be added for one negative charge.
Choosing the central atom
We have to select one atom as the central atom because around the central atom all the atoms are connected via a covalent bond and geometry will be predicted. Based on the size and electropositivity we select C as the central atom here. C has a larger size than H and O atoms and is more electropositive than both.
Satisfying the octet
Every individual atom in the CHO- should be satisfied by their octet to fulfill their valence shell. The electronic configuration of C, O, and H are [He]2s22p2, [He]2s22p4, and 1s1. So, C and O need 8 electrons as they are p block elements. So, the total electrons required according to the octet, 8+8+2 = 18.
Satisfying the valency of every atom
C is tetravalent, whereas O is di and H is monovalent according to the electrons in their respective valence shell. According to the octet, the electrons required are 18 whereas the total valence electrons are 12. So, we need 18-12 = 6 more electrons or 6/2 = 3 bonds to satisfy the valency of each atom.
Assign the lone pairs
After satisfying the octet as well as valency of each atom present in the molecule we should assign the non-bonded electrons for each respective atom. After the two bonds formation O has four more non-bonded electrons, which exist as lone pairs over the O atom. C and H have no lone pairs.
2. CHO- lewis structure shape
The shape of every molecule is depending upon the atoms present within it and is also responsible for any kind of repulsion. Let us discuss the shape of CHO- in detail.
The shape of the CHO- is trigonal planar. This geometry also favors the central atom hybridization value, which is sp2. CHO- is AX2 type molecule and according to the VSEPR (Valence Shell Electrons Pair Repulsion) theory, the geometry of AX2 is trigonal planar if there are no lone pairs over the central atom.
If there is any bulky group will be present at the vacant site of C then there is a chance of steric repulsion between that bulky group and the H atom. Although H is very small in size, due to that steric repulsion maybe the geometry will no longer be trigonal planar and also deviated from the ideal shape.
3. CHO- valence electrons
Valence electrons are those electrons present in the outermost orbital of every atom in the molecule. Now count the total number of valence electrons for CHO- molecule.
The total number of valence electrons for CHO- is 12. The electronic configuration of C, O, and H are [He]2s22p2, [He]2s22p4, and 1s1. So, C, O, and H have 4, 6, and 1 valence electrons in their respective valence orbital. For C and O the valence orbitals are 2s and 2p and for H it is 1s.
- Now calculate the overall valence electrons for CHO-
- Valence electrons for C is 4
- Valence electrons for O is 6
- The valence electron for H is 1
- For extra negative charge is 1
- So, the total valence electrons of CHO- are 4+6+1+1 = 12.
4. CHO- lewis structure lone pairs
Lone pairs are non-bonded electrons that are present over the outermost orbital but not involved in bond formation. Now we see which atom has lone pairs.
Only O contains lone pairs in the CHO- molecule. From the electronic configuration O, it is evident that there are six electrons in the outermost orbital of O. But here O makes two bonds with C by sharing two electrons, so it has the rest of the four electrons exist as two pairs of lone pairs.
- Lone pairs are to be calculated by the formula, lone pairs = valence electrons – bonded electrons.
- The lone pairs over the C atom are, 4-4 = 0
- The lone pairs over O are, 6-2 = 4
- The lone pairs over the H atom are, 1-1 = 0
- So, from the above calculation, we can say that only the O atom carries 4 lone pairs which means two pairs of lone pairs are present over the O atom only.
5. CHO- lewis structure angle
The bond angle is the angle made by atoms in the molecule for the perfect alignment of atoms to avoid any repulsion. Let us predict the bond angle of the CHO- molecule.
The bond angle of CHO- is 1200. This bond angle is shown in the trigonal planar molecule. CHO- is a trigonal planar molecule so the bond angle around central C is 1200. According to the VSEPR theory, the bond angle of AX2 type molecule is always 1200 if there is no deviation factor present.
There is no steric crowding is present within the aldehyde so the bond angle is perfect 1200 as per trigonal planar geometry. If any bulky group is present in the aldehyde as an alkyl part then there will be a chance of steric repulsion as well as a change of bond angle too.
6. CHO- lewis structure formal charge
The formal charge is a hypothetical concept, by this, we can predict the charge that appears on the molecule. Let us calculate the formal charge in the following section.
The formal charge of CHO- is not zero because there is one negative charge already present within the molecule. Now we have to check the individual formal charge of each atom present in CHO-. We have to assume that there is the same electronegativity for all the atoms present in the CHO- of a formal charge.
- The formula being used for the formal charge is, F.C. = Nv – Nl.p. -1/2 Nb.p.
- The formal charge over C is 5-0-6 = -1
- The formal charge over O is 6-4-(4/2) = 0
- The formal charge over H is, 1-0-(2/2) = 0
- So, from the above calculation, it is evident that CHO- carries one charge and the charge is present over the C atom and the charge is negative.
7. CHO- lewis structure octet rule
Every atom in the molecule will obey the octet rule by fulfilling its outermost orbital and accepting a suitable number of electrons. Now we see how CHO- follows the octet rule.
To complete the octet rule C and O shared electrons in their valence shell. They are p block elements so they need eight electrons , whereas H needs two in its valence orbital as it is an s block element. C makes four bonds by sharing eight electrons whereas O makes a double bond to complete their octet.
From the electronic configuration of every atom, we can see that the p block element needs eight electrons (two in s and six in p orbitals). Again, s block element needs two electrons. By sharing bonds all the atoms fulfill their respective valence orbital and obey the octet rule.
8. CHO- lewis structure resonance
Resonance is the delocalization of electron clouds between different skeleton forms of the molecule. Now learn about the CHO- resonance in brief in the following section.
There are different numbers of resonating structures that occur in the CHO- molecule.
- There are enough electron clouds are present which can be delocalized within the molecule in different skeleton forms.
- There is a double bond present between C and O and also negative charge is also present.
Both structures I and II are the resonance structures of the CHO-. Among both only structures, I is more stable than structure II because structure I have a more covalent bond. Structure II has a lower number of covalent bonds but the negative is also present over the electronegative O atom.
9. CHO- hybridization
Hybridization is the mixing of orbitals to form a new hybrid orbital of equivalent energy to form a covalent bond. Now discuss the hybridization of CHO- in the brief.
From the below table it is shown that hybridization of central C in CHO- is sp2 hybridized.
| Structure | Hybridization value | State of hybridization of central atom | Bond angle |
| Linear | 2 | sp /sd / pd | 1800 |
| Planner trigonal | 3 | sp2 | 1200 |
| Tetrahedral | 4 | sd3/ sp3 | 109.50 |
| Trigonal bipyramidal | 5 | sp3d/dsp3 | 900 (axial), 1200(equatorial) |
| Octahedral | 6 | sp3d2/ d2sp3 | 900 |
| Pentagonal bipyramidal | 7 | sp3d3/d3sp3 | 900,720 |
The s and p orbital of C are involved in the hybridization. We can calculate the hybridization by the convention formula, H = 0.5(V+M-C+A), where H= hybridization value, V is the number of valence electrons in the central atom, and M = monovalent atoms surrounded.
10. CHO- solubility
CHO is an organic functionality, so it is soluble in an organic solvent. Let’s discuss the solution of CHO- solubility.
The list of solutions where CHO can be soluble,
- Benzene
- Toluene
- CCl4
- Chloroform
- Methanol
- Ethanol
Why and How is CHO- soluble in the above solution?
An organic molecule is non-polar or slightly polar, so they have low solubility in the polar solvent.
CHO- is soluble in above solution as it has a greater solubility. But it has a lower solubility than a water molecule, with temperature the solubility will be increased. The organic solvent does not make any H bond so the solubility will be lower.
11. Is CHO- ionic?
According to Fajan’s rule, no molecule is 100% covalent or ionic, it is depending on the ionic potential and nature of the bond. Let’s see if CHO is ionic or covalent.
CHO- is a not a ionic rather covalent molecule. It shares electrons among the atoms. CHO is an organic molecule and all organic molecule is covalent because hydrocarbon molecule is made by electron sharing between C and H atoms.
Why and How CHO- is covalent?
There will be electron sharing between bonds among the CHO- molecule making the covalent.
CHO- is covalent because the ionic potential of C is very low and the polarizability of O is also very small. So, there is no chance for this molecule to make ionic. CHO- is an organic molecule and shares electrons between C and O atoms. Sharing electrons makes the bond covalent.
The C center is electrophilic due to electrons being dragged away toward the O site.
12. Is CHO- acidic or basic?
The acid or basic nature of a molecule depends on the releasing ability of proton as well as OH–. Let see whether CHO- is acidic or basic.
CHO- is slightly acidic. It is more acidic than ketone or any other neutral organic functionality. It depends on the poor electron-donating effect of aldehyde and the lower value of pka makes the molecule acidic.
Why and how CHO- is acidic?
The acidic nature of any molecule is depending on the ability to donate H+ ions according to the Arrhenius theory.
CHO- is slightly acidic because the proton is not attached to any electronegative atom, which can able to draw the electron density towards it. But there a double bonded O is present with a C atom where H is attached. The electron density of C is being dragged away by the O and making the H slightly acidic.
Also, from the experimental data, we can see that the pka value of aldehyde is very lower. If there is -I containing Alkyl group is present then it increases the acidity of the molecule. Again, the +R containing group decreases the acidity as well.
13. Is CHO- polar or nonpolar?
The polarity of a molecule is solely dependent on the value of the dipole moment of the molecule. Now see whether CHO is polar or not.
CHO- is a polar molecule. The main reason behind its polarity is that there is a permanent dipole-moment is present in the molecule, again the electronegativity difference between C and O is enough to create a resultant dipole moment. So, it can soluble in water for its polarity.
Why and how CHO- is polar?
The permanent resultant dipole-moment makes CHO- polar. Now discuss its polarity in brief in the following section.
CHO- is polar because the dipole-moment acts from electropositive C to electronegative O atom via sigma and π bonds. There is no other dipole moment that can work, so there is no chance to cancel out the previous dipole moment and for this reason, a permanent resultant dipole moment will be observed.
Due to this polarity C-O bond is also polar and for this reason, it can be soluble in polar solvents like water, DMSO, etc. The higher the polarity of the bond higher will be chance of the ionic nature of the bond, so we can also say that the C-O bond has partial ionic character than the C-H bond.
14. Is CHO- tetrahedral or lienar?
The shape of the molecule is dependent on the VSEPR theory and the presence of surrounding atoms. Let us discuss whether the CHO- is tetrahedral or not.
The geometry of the CHO- is not tetrahedral rather trigonal planar. Because it is an AX2 type of molecule and according to VSEPR theory AX2 molecule always adopts a trigonal planar shape. Only AX3 type molecule adopts tetrahedral geometry.
Why and How CHO- is not tetrahedral or linear?
Planar geometry molecule cannot be a tetrahedral shape. Now discuss how CHO- adopts trigonal planar shape.
CHO- is not tetrahedral as a molecule adopts a trigonal planar shape when it has three surrounding atoms. In CHO- there are two surrounding atoms, according to VSEPR theory. There is also a double bond present between C and O. So, it adopts a trigonal planar shape.
Again, from the hybridization value, we can say that sp2 hybridized molecules always adopt trigonal planar geometry. For sp hybridized molecule adopts linear and sp3 adopts tetrahedral shape if there is no deviation factor is present.
Conclusion
CHO- is a trigonal planar molecule with sp2 hybridized of the central atom. It is a neutral molecule but the C center is more electron deficient and prone to nucleophilic attack rapidly. C -O bond is polar and for this polarity, it can soluble in polar solvent although it is an organic molecule.
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Hi……I am Biswarup Chandra Dey, I have completed my Master’s in Chemistry from the Central University of Punjab. My area of specialization is Inorganic Chemistry. Chemistry is not all about reading line by line and memorizing, it is a concept to understand in an easy way and here I am sharing with you the concept about chemistry which I learn because knowledge is worth to share it.