Organic Chemistry 315 Exam I

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Questions and Answers

What is the correct formula of the molecule represented in the provided diagram containing OH and NH2 groups?

C16H23BrClNO

C15H25BrClNO2 (correct)

C15H23BrClNO2

C16H23ClBrNO2

What is the double bond equivalent (DBE) of the molecule that contains Cl and NH2?

7 (correct)

Which of the following molecules is NOT aromatic?

A molecule with a complete octet on all atoms

A molecule with sp3 hybridized carbons (correct)

A cyclic molecule with alternating double bonds

A molecule containing multiple resonance structures

Which statement about chemical analysis techniques is true?

The chemical shift in 1H NMR is influenced by the solvent used. Signup and view all the answers

In NMR spectroscopy, what aspect primarily affects the chemical shift of protons?

The electronegativity of adjacent atoms Signup and view all the answers

Which statement accurately describes the application of high-resolution mass spectrometry?

It can differentiate ortho-, meta-, and para-dichlorobenzene effectively. Signup and view all the answers

What characteristic of carbon NMR spectroscopy is NOT true?

It can observe more than just 13C isotopes in samples. Signup and view all the answers

What is the key reason that lighter atoms exhibit higher vibrational frequencies in IR spectroscopy?

They have lower mass and thus vibrate faster. Signup and view all the answers

Which molecular orbital of the aldehyde is filled by the electron pair from the alcohol during the formation of a hemiacetal?

σ Signup and view all the answers

In the context of decreasing pKaH, which is the correct ranking of I-IV?

pKaH II > I > III > IV Signup and view all the answers

How do structures I and II relate to each other?

I and II are resonance structures with varying electron cloud distribution. Signup and view all the answers

Which compound is likely to have the lowest activation energy in its cyclization rate-determining step?

O with H and Cl Signup and view all the answers

Among the π molecular orbitals of 1,3,5,7-octatetraene, which orbital has the highest energy?

Orbital g Signup and view all the answers

What is the nature of the bond formed between the aldehyde and alcohol during hemiacetal formation?

Covalent bond Signup and view all the answers

Which species acts as a nucleophile in the formation of a hemiacetal from an aldehyde?

The alcohol oxygen Signup and view all the answers

What characteristic do the compounds in question 8 share that affects their rate of cyclization?

Type of substituents Signup and view all the answers

Which orbital has the second lowest energy?

p orbital Signup and view all the answers

How many nodes does the 'h' orbital have?

3 Signup and view all the answers

Which orbital is typically referred to as the LUMO?

s orbital Signup and view all the answers

In terms of acidity, which of the following compounds has the lowest pKa?

Cl Signup and view all the answers

Which compound is more acidic between OH and NH2?

OH Signup and view all the answers

In a 13C NMR spectrum, what would indicate a unique signal?

Different environments for carbon atoms Signup and view all the answers

Which reaction mechanism would produce an aromatic compound?

Electrophilic aromatic substitution Signup and view all the answers

What is the major product when hydroxyl (-OH) reacts with PCC?

Aldehyde Signup and view all the answers

What is the pKa range for a typical alkane?

50-60 Signup and view all the answers

How does resonance affect the pKa of compounds like acetone and acetylacetone?

Resonance stabilizes the conjugate base, leading to a lower pKa. Signup and view all the answers

Which compound has the lowest pKa value among those listed?

Acetylacetone Signup and view all the answers

Why does fluorene have a significantly lower pKa than 9,10-dihydroanthracene?

Fluorene has a more stable conjugate base due to its structure. Signup and view all the answers

What does the degree of unsaturation (DBE) indicate in the molecular formula C10H10O2?

The number of rings and double bonds present. Signup and view all the answers

Which structure corresponds to o-dichlorobenzene?

Chlorine atoms at the 1 and 2 positions of the benzene ring Signup and view all the answers

Which structure is representative of p-dichlorobenzene?

Chlorine atoms at the 1 and 4 positions of the benzene ring Signup and view all the answers

What is the significance of formal charge in molecular structures?

It helps in predicting the reactivity and stability of the molecule. Signup and view all the answers

Which structure has the correct formal charge for the nitrogen atom?

Formal charge of 0 when it has two bonds and one lone pair Signup and view all the answers

Which 13C NMR spectrum corresponds to acetylsalicylic acid?

The spectrum shows distinct peaks at $200\text{ ppm}$ and $160\text{ ppm}$ Signup and view all the answers

What is an incorrect interpretation of the 13C NMR spectrum for acetylsalicylic acid?

All peaks in the spectrum represent equivalent carbon atoms. Signup and view all the answers

In NMR spectroscopy, what does a higher ppm value typically indicate?

The presence of electronegative substituents Signup and view all the answers

Which of the following statements about acetylsalicylic acid is true?

It has a molecular formula of C9H8O4. Signup and view all the answers

Study Notes

Exam Information

Exam I for Organic Chemistry 315 will be held on October 7, 2024.
Students must fill out all required information on the exam sheet neatly and legibly.
Students must print their first and last name on every page.
Students must read and sign the pledge prior to submitting the exam.

Multiple Choice Questions

Question 1: The correct formula for the given molecule is C16H23BrClNO2.
Question 2: The double bond equivalent (DBE) of the molecule is 7.
Question 3: The molecule in option E is not aromatic.
Question 4: The true statement is "Mass-spectrometry is a technique that measures the mass-to-charge ratio of either positive ions or negative ions."
Question 5: The structure in option B has the correct formal charge assigned.
Question 6: The correct 13C NMR spectrum of acetylsalicylic acid is A.
Question 7: The order of decreasing pKa values of the compounds is pKaH I > II > IV > III.
Question 8: When an aldehyde reacts with an alcohol to form a hemiacetal, the electron pair from the alcohol fills the π molecular orbital* of the aldehyde.
Question 9: Structures I and II are resonance structures with different electron cloud distribution.
Question 10: The compound in option A has the lowest activation energy for cyclization.

Open Ended Questions

Question 11:
- Orbital g has the highest energy.
- Orbital a has the second lowest energy.
- Orbital h has 3 nodes.
- Orbital g is the LUMO.
Question 12:
- 1) CH3CH2OH
- 2) NH3
- 3) CH3COOH
- 4) CH3CH2Cl
- 5) CH3CH2OH
- 6) CF3CH2OH
- 7) N(CH3)3
- 8) H2O
Question 13:
- The resonance structure of molecule (a) shows the lone pair of electrons on the nitrogen atom moving to form a double bond with the adjacent carbon atom, while the double bond between carbon and oxygen becomes a single bond with the negative charge being placed on the oxygen atom.
- The resonance structure of molecule (b) shows the lone pair of electrons on the oxygen atom moving to form a double bond with the adjacent carbon atom, while the double bond between carbon and oxygen becomes a single bond with the negative charge being placed on the oxygen atom.
Question 14:
- a) The product is phenol.
- b) The product is benzoic acid.
- c) The product is benzaldehyde.
Question 15:
- The number of signals in the 13C NMR spectrum of the first molecule is 4.
- The number of signals in the 13C NMR spectrum of the second molecule is 6.
- The number of signals in the 13C NMR spectrum of the third molecule is 5.
Question 16:
- The mechanism of the transformation involves protonation of the carbonyl oxygen of the ketone, followed by nucleophilic attack of the hydroxyl group on the carbonyl carbon, leading to the formation of a hemiacetal.
Question 17:
- The lower pKa values of the compounds are due to the stabilization of their conjugate bases by resonance.
  - The conjugate base of 9,10-dihydroanthracene is stabilized by resonance delocalization of the negative charge into the aromatic ring.
  - The conjugate base of fluorene is stabilized by resonance delocalization of the negative charge into the two aromatic rings.
  - The conjugate base of acetone is stabilized by resonance delocalization of the negative charge into the carbonyl group.
  - The conjugate base of acetylacetone is stabilized by resonance delocalization of the negative charge into the two carbonyl groups.
- Fluorene has a significantly lower pKa than 9,10-dihydroanthracene because the negative charge in the conjugate base of fluorene can be delocalized into two aromatic rings, while the negative charge in the conjugate base of 9,10-dihydroanthracene can only be delocalized into one aromatic ring, resulting in greater stabilization.
Question 18:
- The molecular structure based on the information provided is 1,2-Dimethoxybenzene.
- The structure is shown in the provided rectangular box.

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Prepare for your Organic Chemistry 315 Exam I with this quiz! This assessment includes essential concepts such as molecular formulas, double bond equivalents, and mass-spectrometry techniques. Test your knowledge and readiness ahead of the exam on October 7, 2024.