Question

ONLY DO PART 2. USE PART 1 WHILE GETTING PART 2'S ANSWER. THANK YOU.

(PART 1:) Conformations of 2,2,4,4-tetramethylpentane Sight down the C2-C3 bond and draw the six conformations of the molecule (Newman Projections) and identify the unique conformations. Identify the types and degrees of strain in each unique conformer Sketch an approximate potential energy diagram (for dihedral angles from 0-300o )

(PART 2:)

Make the most stable conformer of this molecule using ChemMagic Model Kit. OPTIMIZE the structure three times and record its energy. Measure all C-C bond lengths and C-C-C bond angles in this molecule. Make sure to measure the structure AFTER you OPTIMIZE. Are there any bond angles and/or bond lengths which are significantly different (±5%) from the average values for these types of bonds? (Hint: Calculate 5% of the typical bond measurements Table 1 below, and find the acceptable variation range) If there are, give your reasons for why these particular bond lengths and/or angles different from the average values?

Answer 1

Data obtained from chem magic model kit:

• Energy = 132.292 kJ
• C-C bond length = 154 pm ( for the terminal C-C bond)
• C-C bond length = 157 pm ( for the internal C-C bond)
• C-C-C bond angle = 107.9 ^o , 107.1 ^o , 109.5^o , ( for the terminal C-C-C bond)
• C-C-C bond angle = 122.5 ^o  ( for the internal C-C-C bond)
• We are able to see variation in internal C-C Bond lengths and in internal C-C-C bond angles. The main factor behind this variation from normal value is steric repulsion. due to the presence of 4 methyl branches in this pentane molecule internal C-C bond is longer than expected. For keeping these bulk groups apart the internal bond angle is more opened to 122.5 ^o ( which is higher than a normal tetrahedral angle)