MCAT Biology : Covalent Bonds and Hybrid Orbitals
Study concepts, example questions & explanations for MCAT Biology
All MCAT Biology Resources
Example Questions
Example Question #21 : Covalent Bonds And Hybrid Orbitals
Which compound contains the most stable carbon bonds?
Ethene
Methane
Acetone
Carbon dioxide
Carbon dioxide
The stability of a bond can be compared to others by determining the hybridization of the bond. It helps to remember that the bond with the most s character is considered the most stable.
Carbon dioxide has a carbon that is connected to two oxygens by two double bonds. This means that the carbon has sp hybridization. Since the bond has 50% s character, it is the most stable out of the available compounds.
Methane contains only single bonds and will have an sp3 hybridized carbon, with only 25% s character. Acetone and ethene each contain one double bond and will contain an sp2 hybridized carbon with 33% s character.
Example Question #22 : Covalent Bonds And Hybrid Orbitals
The compound below is reacted with 
The initially chiral carbon has an 
Example Question #23 : Covalent Bonds And Hybrid Orbitals
Which compound will have the highest bond energy?
The carbon-carbon bond in benzene.
The carbon-hydrogen bond in methane.
The carbon-carbon bond in ethane.
The carbon-carbon bond in ethene
The carbon-carbon bond in ethene
In organic chemistry, the trend is that bond length is inversely proportional to bond energy. Shorter bonds result in a higher bond energy. The double bond in ethene is the shortest bond out of all the others. As a result, it has the highest bond energy.
Note that in benzene there are three double bonds and three single bonds between carbons, however, resonance means that each of these only has partial double bond character, and is therefore longer than a pure double bond.
Example Question #24 : Covalent Bonds And Hybrid Orbitals
A carbon-carbon single bond has an average length of 1.54 Angstroms. A carbon-carbon double bond has an average length of 1.33 Angstroms. Finally, a carbon-carbon triple bond has an average length of 1.20 Angstroms. For the allyl cation shown below, what is the average carbon-carbon bond length?
The allyl cation involves resonance, as the double bond is delocalized; thus, each carbon-carbon bond will have an identical length somewhere between a pure single and pure double bond. The average bond length will be the average of a single bond and double bond, which is 1.44 Angstroms.
Example Question #24 : Covalent Bonds And Hybrid Orbitals
Which compound has the largest bond energy between carbons?
Ethyne
Benzene
Propane
1,3-butadiene
Ethyne
It helps to remember that bond energy is inversely proportional to bond length. In other words, the shorter the bond, the higher the bond energy.
Bond length is shortened when pi bonds are involved, so double and triple bonds are much shorter than simple sigma bonds. The bond length between the carbons in ethyne is the shortest out of all options because they are triple bonded to one another. This also makes it the most stable bond, and gives it the largest bond energy.
Benzene and 1,3-butadiene will have relatively high energy stored in double bonds, but will be unable to match a triple bond. Propane has only single bonds and will have the lowest bond energy of these answers.
Example Question #26 : Covalent Bonds And Hybrid Orbitals
Drain cleaners are a common household staple, used to open clogged drains in bathtubs and sinks. Human hair is a common culprit that clogs pipes, and hair is made predominately of protein. Drain cleaners are effective at breaking down proteins that have accumulated in plumbing. Drain cleaners can be either acidic or basic, and are also effective at breaking down fats that have accumulated with proteins.
A typical reaction—reaction 1—which would be expected for a drain cleaner on contact with human hair, would be as follows in an aqueous solution:
Another reaction that may occur, reaction 2, would take place as follows in an aqueous solution:
The C–N bond in the original protein, before reaction with drain cleaner is __________.
stronger and shorter than the carbonyl bond in the same molecule
stronger and longer than the carbonyl bond in the same molecule
nonpolar due to electron interaction with the lone pair on the N atom
weaker and longer than the carbonyl bond in the same molecule
weaker and shorter than the carbonyl bond in the same molecule
weaker and longer than the carbonyl bond in the same molecule
The C–N bond is a single bond, and the carbonyl bond is a double bond. Double bonds are stronger and shorter than single bonds.
Certified Tutor
All MCAT Biology Resources
