For cyclopropane, depicted below, draw the Newman projection on the template pro

Question

For cyclopropane, depicted below, draw the Newman projection on the template provided. In addition to torsional strain from eclipsing hydrogens indicate another source of ring strain prevalent in this molecule. Draw the molecular orbitals at the carbon centers that contribute to that source of strain on the structure provided at the top. and indicate hybridization state of relevant orbitals. In addition, indicate your estimation of the number of kcal/mol that torsional strain contributes to the overall strain of the molecule. REMEMBER, each eclipsing interaction in ethane is worth 1 kcal/mol. SOURCE OF RING STRAIN?

Explanation / Answer

Cyclopropane is the most strained of all the cycloalkanes because of the angle strain which is caused by the C-C-C bond angle of 60

                                                                                                H             Eclipsed Hydrogen

                             H                                                                H                                                                            

C                       

                                H                                                             H             Eclipsed Hydrogen

                                                                                                H

Newman projection of cyclopropane is shown above where the location of eclipsed Hydrogens is shown for two corresponding Carbon atoms. The neighbouring C-H bonds give rise to torsional strain. And the C-C-C bond angle of 60 gives rise to ANGLE STRAIN.

Although the hybridisation of each Carbon in cyclopropane is sp3 but to obtain a ring structure the overlap of molecular orbitals is such that it gives rise to bent bonds.

                Molecular orbitals in cyclopropane

                                                   H                 H

                                               

                                                                C

                                C                                                             C

                H                                                                                                             H

                                H                                                                             H

Now to evaluate the torsional strain of the molecule we need to see how many eclipsed interactions are happening in the molecule. As shown in the newman projection for two eclipsing hydrogens on 2 corresponding Carbons there is 1 eclipsing interaction since there are a total of 6 Hydrogen on 3 Carbons there should be 6 eclipsing interactions. Also the 3 C-C bonds are eclipsed. So there should be a total of 9 eclipsing interactions. So a total of 9X1kcal/mol=9 kcal/mol of torsional strain in the molecule (given each eclipsing interaction in ethane = 1kcal/mol )

Related Questions

Navigate

• Browse (All)
• Browse F
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.