Open Question
(b) Determine ΔH for the atomization of naphthalene using Hess’s law and the data in Appendix C. (ΔHf° of solid naphthalene is 77.1 kJ/mol and the molar heat of sublimation of naphthalene is 72.9 kJ/mol.)
Ch.9 - Molecular Geometry and Bonding Theories
Chapter 9, Problem 120b
The organic molecules shown here are derivatives of benzene in which six-membered rings are 'fused' at the edges of the hexagons.
(b) Suppose you are given a sample of one of the compounds. Could combustion analysis be used to determine unambiguously which of the three it is?
Verified step by step guidance1
Understand the concept of combustion analysis: Combustion analysis is a method used to determine the elemental composition of a compound by burning the sample and analyzing the resulting products, typically carbon dioxide and water.
Recognize the output of combustion analysis: This technique provides the ratios of carbon, hydrogen, and sometimes other elements like nitrogen or sulfur in the compound, but it does not provide structural or isomeric information.
Consider the structural similarities of the derivatives: If the compounds are isomers (same molecular formula but different structures), combustion analysis will yield the same carbon to hydrogen ratio for each compound, making it impossible to distinguish between them based solely on this analysis.
Evaluate the need for additional analytical techniques: To unambiguously identify which derivative of benzene you have, consider using spectroscopic methods such as NMR (Nuclear Magnetic Resonance) or IR (Infrared Spectroscopy), which can provide information about the molecular structure.
Conclude the suitability of combustion analysis: Determine that while combustion analysis can confirm the elemental composition, it cannot differentiate between structural isomers, and thus, it cannot be used alone to unambiguously identify the specific derivative of benzene in the sample.
Verified Solution
Video duration:
1m
This video solution was recommended by our tutors as helpful for the problem above.Was this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Combustion Analysis
Combustion analysis is a technique used to determine the elemental composition of organic compounds. In this method, a sample is burned in excess oxygen, producing carbon dioxide and water. By measuring the amounts of these products, one can calculate the ratios of carbon and hydrogen in the original compound, which can help identify the compound's structure.
Recommended video:
Guided course
01:29
Combustion of Non-Hydrocarbons
Isomerism
Isomerism refers to the phenomenon where compounds have the same molecular formula but different structural arrangements or spatial orientations. In the context of fused benzene derivatives, isomers can exhibit distinct physical and chemical properties, which may affect their combustion products. Understanding isomerism is crucial for interpreting combustion analysis results.
Recommended video:
Guided course
01:39Isomerism in Coordination Complexes Example
Molecular Formula vs. Structural Formula
The molecular formula indicates the number and types of atoms in a compound, while the structural formula shows how these atoms are arranged. In combustion analysis, knowing the molecular formula is essential, but distinguishing between different structural isomers is necessary to determine the specific compound. This distinction is vital when analyzing combustion products to identify the original compound.
Recommended video:
Guided course
02:08Molecular Formula
Related Practice
Textbook Question
Many compounds of the transition-metal elements contain
direct bonds between metal atoms. We will assume
that the z-axis is defined as the metal–metal bond axis.
(d) Sketch the energylevel
diagram for the Sc2 molecule, assuming that only the
3d orbital from part (a) is important.
353
views
Textbook Question
The organic molecules shown here are derivatives of benzene
in which six-membered rings are 'fused' at the edges
of the hexagons.
(e) Benzene, naphthalene, and anthracene
are colorless, but tetracene is orange. What does this imply
about the relative HOMO–LUMO energy gaps in these molecules?
See the 'Chemistry Put to Work' box on orbitals
and energy.
644
views
Open Question
Antibonding molecular orbitals can be used to make bonds to other atoms in a molecule. For example, metal atoms can use appropriate d orbitals to overlap with the π*2p orbitals of the carbon monoxide molecule. This is called d-π backbonding. (a) Draw a coordinate axis system in which the y-axis is vertical in the plane of the paper and the x-axis horizontal. Write 'M' at the origin to denote a metal atom. (b) Now, on the x-axis to the right of M, draw the Lewis structure of a CO molecule, with the carbon nearest the M. The CO bond axis should be on the x-axis. (c) Draw the CO π*2p orbital, with phases (see the 'Closer Look' box on phases) in the plane of the paper. Two lobes should be pointing toward M. (d) Now draw the dxy orbital of M, with phases. Can you see how they will overlap with the π*2p orbital of CO? (e) What kind of bond is being made with the orbitals between M and C, σ or π? (f) Predict what will happen to the strength of the CO bond in a metal–CO complex compared to CO alone.
Textbook Question
Methyl isocyanate, CH3NCO, was made infamous in 1984 when an accidental leakage of this compound from a storage tank in Bhopal, India, resulted in the deaths of about 3800 people and severe and lasting injury to many thousands more. (a) Draw a Lewis structure for methyl isocyanate.
970
views