A hydrogen bond is an intermolecular attractive force stronger than the Van der Waals force. This force affects several physical, chemical, and biological shapes, nature, and reactivity properties.
In order to represent a hydrogen bond, dash or dotted lines (....) are used. These lines indicate that a hydrogen atom is sandwiched between two electronegative atoms.
The first common mistake a student can make is assuming any electronegative atom can form a Hydrogen bond. In the chapter Hydrogen bond, I have explicitly mentioned that only highly electronegative atoms like Nitrogen (N), Oxygen (O), and Fluorine (F) can form Hydrogen bonds. (Though there are special circumstances where exceptions are possible.)
This means that several functional groups, such as acid, amide, aldehyde, haloalkane, and amine, can be explored when studying Hydrogen bonds.
Let us use an aldehyde like acetaldehyde (CH3CHO) and alcohol like ethanol (CH3CH2OH) as an example to draw a Hydrogen bond.
1) The first step is to draw them.
2) The next step is identifying Hydrogen bond donors and the Hydrogen bond acceptors in each molecule. I have mentioned in the chapter what characteristics to look for in donors and acceptors of the Hydrogen bond.
In this case, the Hydrogen atom covalently linked to the electronegative Oxygen atom works as a Hydrogen bond donor, while the lone pair on the Oxygen atom acts as the Hydrogen bond acceptor.
The second common mistake that a student can make is assigning the Hydrogen atom of the acetaldehyde as a Hydrogen bond donor. It is crucial to note that a Hydrogen atom must be covalently bonded to the O, N, or F atom to serve as a Hydrogen bond donor.
3) The next step is to place the H-bond donor and acceptor groups in a way that they form a Hydrogen bond.
There are several ways to accomplish this, and I will list a few below. However, only one of these representations is correct (marked in green).
One important concept covered in the chapter is the impact of bonding angle on the strength of Hydrogen bonds. The ideal bond angle is 180o, which occurs when the Hydrogen donor atom and the lone pair of the acceptor atom are in a straight line. When the angle decreases, the strength of the H-bond also decreases, and no bonds are formed when the angle is 90o or less. Additionally, a common mistake is drawing the Hydrogen bonds at an angle less than 180o.
Overall, there are several ways in which students can misinterpret the simple concept of understanding and drawing an H-bond. However, it is important to remember that Hydrogen bonding is a crucial force that holds our DNA in shape and helps bind enzymes to their receptors. By learning and applying this concept correctly, we can give Hydrogen bonding the recognition it deserves.