Advanced Organic Chemistry: Carbon-13 NMR spectrum of 1-iodobutane CH3CH2CH2CH2I

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Interpreting and explaining the Carbon-13 13C NMR spectrum of 1-iodobutane (butyl iodide) CH3CH2CH2CH2I

[Author © Dr Phil Brown GRIC, PhD: Doc Brown's advanced level organic chemistry exam revision notes suitable for students of UK A level chemistry courses & US K12 grade 11, grade 12 and AP honors chemistry courses: Molecular spectroscopy analysis of 1-iodobutane (13C NMR spectra) [spectra page updated RE-EDIT]

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 C-13 NMR spectroscopy - spectra index

See also comparison of the infrared, mass, 1H NMR and 13C NMR spectra of the four isomers of C4H9I

and Isomers of molecular formula C4H9X  (where X = F, Cl, Br or I and basic data on NMR chemical shifts)

Practise exam questions based on the 13C NMR spectrum of 1-iodobutane

Introductory note on the 13C NMR spectrum of 1-iodobutane

Students and teachers please note that my explanation of the carbon-13 NMR spectrum of 1-iodobutane is designed for advanced, but pre-university, chemistry courses.

The description does not involve the chemical shift δ spin-spin coupling effects for 1-iodobutane and the relative size of the carbon-13 NMR shifts does not give the ratio of the carbon atoms in the different non-equivalent chemical environments of the 1-iodobutane molecule.

The most common solvent used for investigating the 13C NMR spectrum of compounds like 1-iodobutane, is CDCl3 and other deuterated solvents.

13C nmr spectrum of 1-iodobutane C4H9I CH3CH2CH2CH2I analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of 1-iodobutane C13 carbon-13 nmr doc brown's advanced organic chemistry revision notes 

TMS is the acronym for tetramethylsilane, formula Si(CH3)4, whose 13C atoms are arbitrarily given a chemical shift of 0.0 ppm. This is the 'standard' in 13C NMR spectroscopy and all other 13C resonances, called chemical shifts, are measured with respect to the TMS, and depend on the individual (electronic) chemical environment of the 13C atoms in an organic molecule - 1-iodobutane here.

1-iodobutane, (n-butyl iodide), C4H9I, CH3-CH2-CH2-CH2-I

The molecular structure and naming of haloalkanes

Interpreting the C-13 NMR spectrum of 1-iodobutane

As you can see from the diagram above there are 4 different 13C chemical shift lines in the C-13 NMR spectrum of 1-iodobutane indicating 4 different chemical environments of the 4 carbon atoms of 1-iodobutane.

CH3CH2CH2CH2I

(Note the 4different colours indicating the 4 different chemical environments of the 4 carbon atoms in 1-iodobutane).

13C chemical shifts (a) to (d) on the C-13 NMR spectrum diagram for 1-iodobutane.

(a)  CH3CH2CH2CH2I : 13C NMR chemical shift of 13.0 ppm for the methyl group carbon atom.

(b)  CH3CH2CH2CH2I : 13C NMR chemical shift of 23.6 ppm for the carbon atom of the 'left' CH2 group.

(c)  CH3CH2CH2CH2I : 13C NMR chemical shift of 35.5 ppm for the carbon atom of the 'right' CH2 group.

(d)  CH3CH2CH2CH2I : 13C NMR chemical shift of 6.7 ppm for the carbon atom bonded to the iodine atom.

The carbon-13 NMR spectra provides direct evidence of 4 different carbon atom environments for the 4 carbon atoms in the 1-iodobutane molecule, deduced from the presence of 4 different 13C NMR chemical shifts (ppm).

There are no equivalent carbon atoms in 1-iodobutane.
QUESTIONS

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Q1 How many distinct ¹³C NMR signals are observed for 1‑iodobutane?

A. 2     B. 3     C. 4    D. 5

Q2 What is the relative integration pattern in a standard broadband‑decoupled ¹³C NMR spectrum of 1‑iodobutane?

A. All signals integrate equally

B. 3 : 2 : 2 : 2

C. 1 : 1 : 1 : 1

D. 4 : 3 : 2 : 1

Q3 Which carbon appears furthest downfield (highest ppm) in the ¹³C NMR of 1‑iodobutane?

A. CH3– carbon

B. CH3–CH2– carbon

C. –CH2–CH2– carbon

D. –CH2–I carbon

Q5 How many 13C NMR signals does 2‑iodobutane (CH3–CHI–CH2–CH3) show?

A. 2     B. 3     C. 4     D. 5

Q6 Which statement correctly describes 1‑iodobutane and 2‑iodobutane using ¹³C NMR?

A. 1‑iodobutane has 3 signals; 2‑iodobutane has 4

B. 1‑iodobutane has 4 signals; 2‑iodobutane has 3

C. Both have 4 signals

D. Both have 3 signals

Q7 Which isomer of C4H9I has the fewest ¹³C NMR signals?

A. 1‑iodobutane

B. 2‑iodobutane

C. 1‑iodo‑2‑methylpropane

D. 2‑iodo‑2‑methylpropane

Q8 – number of signals in 1‑iodo‑2‑methylpropane

For 1‑iodo‑2‑methylpropane (CH3–CH(CH3)–CH2Br), how many ¹³C NMR signals are expected?

A. 2     B. 3     C. 4    D. 5

Q9 A compound with formula C4H9I shows only 2 signals in its 13C NMR spectrum. Which structure is most consistent?

A. 1‑iodobutane

B. 2‑iodobutane

C. 1‑iodo‑2‑methylpropane

D. 2‑iodo‑2‑methylpropane

Q10 You have an unknown C4H9I that shows 3 distinct ¹³C signals. Which structure is most likely?

A. 1‑iodobutane

B. 2‑iodobutane

C. 1‑iodo‑2‑methylpropane

D. 2‑iodo‑2‑methylpropane

If you think there are any errors, please email me asap at chem55555@hotmail.com

Comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 4 halogenoalkane isomers of C4H9I

NOTE: The images are linked to their original detailed spectral analysis pages AND can be doubled in size with touch screens to increase the definition to the original 1-iodobutane, 2-iodobutane, 1-iodo-2-methylpropane and 2-iodo-2-methylpropane image sizes.  These four molecules are structural isomers of molecular formula C4H9I and exemplify the infrared, mass, 1H NMR and 13C NMR spectra of lower aliphatic halogenoalkanes (haloalkanes, alkyl halides, iodoalkanes, alkyl iodides).

INFRARED SPECTRA (above): Apart from the significant differences in the fingerprint region at wavenumbers 1500 to 400 cm-1, there are no other great striking differences, but each could be identified from its infrared spectrum.

MASS SPECTRA (above): All four give the parent molecular ion of m/z 184, but it is only a relatively tiny peak for 2-iodo-2-methylpropane. All four give the base ion peak of m/z 57. All four give prominent peaks for m/z ions 29 and 41 and all give a tiny peak from an ionised iodine atom at m/z 127. They look quite similar to me and lack a clear fingerprint fragmentation pattern.

1H NMR SPECTRA (above): The 1H NMR spectra of all three molecules give different proton ratios i.e.1-iodobutane four peaks 3:2:2:2, 2-iodobutane four peaks 3:3:2:1, 1-iodo-2-methylpropane three peaks 6:2:1 and 2-iodo-2-methylpropane one peak '1' (effectively no ratio involved), so all four molecular structures can be distinguished from each other by their 1H NMR spectra proton ratios, numbers of peaks and (n+1) rule splitting patterns.

13C NMR SPECTRA (above): The 13C NMR spectra of the four molecules show various numbers of carbon-13 chemical environments i.e 1-iodobutane and 2-iodobutane show four 13C NMR resonances, 1-iodo-2-methylpropane three 13C NMR resonances and 2-iodo-2-methylpropane only two 13C resonances. Therefore 1-iodo-2-methylpropane and 2-iodo-2-methylpropane can be distinguished from the other three by their number of resonances in their 13C NMR spectra, but 1-iodobutane and 2-iodobutane cannot be distinguished from each other from their number of 13C NMR resonance lines - other data would be required.

Key words & phrases: isomer of molecular formula C4H9I CH3CH2CH2CH2I Interpreting the C-13 NMR spectra of 1-iodobutane, 13C nmr spectrum of 1-iodobutane, understanding the carbon-13 nmr spectrum of 1-iodobutane, explaining the line pattern in the high resolution C-13 nmr spectra of 1-iodobutane, revising the C-13 nmr spectrum of 1-iodobutane, ppm chemical shifts of the C-13 nmr spectrum of 1-iodobutane, how to construct the diagram of the C-13 nmr spectrum of 1-iodobutane, how to analyse the chemical shifts in the carbon-13 NMR spectrum of 1-iodobutane deducing the chemical environment of all the carbon atoms in 1-iodobutane examining the c13 nmr spectrum of  1-iodobutane analysing the 13C nmr spectrum of 1-iodobutane how do you sketch and interpret the C-13 NMR spectrum of 1-iodobutane interpreting interpretation of the C-13 NMR spectrum of 1-iodobutane assignment of chemical shifts in the 13C NMR spectrum of 1-iodobutane type functional group haloalkane halogenoalkane alkyl bromide n-butyl iodide Molecular structure diagram of the carbon-13 NMR diagram for the 13C NMR spectrum of 1-iodobutane. Deducing the number of different chemical environments of the carbon atoms in the 1-iodobutane molecule from the 13C chemical shifts in the carbon-13 NMR spectrum of 1-iodobutane. Revision notes on the carbon-13 NMR spectrum of 1-iodobutane. Matching and deducing the structure of the 1-iodobutane molecule from its 13C NMR spectrum. Carbon-13 NMR spectroscopy of halogenoalkanes iodoalkanes, 13C NMR spectra of 1-iodobutane, an isomer of molecular formula C4H9I How do you interpret the chemical shifts of the C-13 NMR spectrum of 1-iodobutane How to interpret the C-13 NMR spectrum of 1-iodobutane Explanatory diagram of the 13C C-13 carbon-13 NMR spectrum of the  number of different carbon atom environments in the 1-iodobutane molecule from its carbon-13 NMR spectrum to help work out the molecular structure of the 1-iodobutane molecule? The uses and distinctive features of the carbon-13 NMR spectrum of the 1-iodobutane molecule explained. What do the number and values of the chemical shifts from the c-13 carbon-13 NMR spectrum tell us about the 1-iodobutane molecule? explaining the decoupled carbon-13 NMR spectrum of 1-iodobutane  with a detailed interpretation diagram of all the C-13 chemical shifts and intensities

Links associated with 1-iodobutane

The chemistry of HALOGENOALKANES (haloalkanes) revision notes INDEX

The infrared spectrum of 1-iodobutane (n-butyl iodide)

The mass spectrum of 1-iodobutane (n-butyl iodide)

The H-1 NMR spectrum of 1-iodobutane (n-butyl iodide)

C-13 NMR spectroscopy index

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ANSWERS

Advanced A-level chemistry - practise exam questions on

If you think there are any errors, please email me asap at chem55555@hotmail.com

I don't mind if students/teachers do a selected printout of these questions and answers.

Q1 How many distinct ¹³C NMR signals are observed for 1‑iodobutane?

A. 2     B. 3     C. 4    D. 5

Answer: C

Explanation: Carbons:

  • C‑1: CH3–
  • C‑2: CH3–CH2–
  • C‑3: –CH2–CH2–
  • C‑4: –CH2–I All are in different environments → 4 signals.

Misconception: Thinking the two internal CH2 carbons are equivalent; they are not, because one is closer to I.

Q2 What is the relative integration pattern in a standard broadband‑decoupled ¹³C NMR spectrum of 1‑iodobutane?

A. All signals integrate equally

B. 3 : 2 : 2 : 2

C. 1 : 1 : 1 : 1

D. 4 : 3 : 2 : 1

Answer: C

Explanation: ¹³C NMR is usually not quantitative at school level; each distinct carbon gives one signal, often treated as equal intensity → 1 : 1 : 1 : 1.

In the 13C NMR spectrum for 1-iodobutane I obtained, the four intensities are similar, but is NOT an integration rule which applies to 1H NMR spectra.

Misconception: Transferring ¹H NMR integration ideas (3H, 2H, etc.) directly to ¹³C NMR.

Q3 Which carbon appears furthest downfield (highest ppm) in the ¹³C NMR of 1‑iodobutane?

A. CH3– carbon

B. CH3–CH2– carbon

C. –CH2–CH2– carbon

D. –CH2–I carbon

Answer: D

Explanation: The carbon directly bonded to I is most deshielded → highest ppm.

Misconception: Assuming the terminal CH3 carbon is most downfield; it is usually most upfield.

Q5 How many ¹³C NMR signals does 2‑iodobutane (CH3–CHI–CH2–CH3) show?

A. 2     B. 3     C. 4     D. 5

Answer: C

Explanation: Carbons:
  • Two different CH3 groups (ends) → 2 signals
  • CHI (chiral centre) → 1 signal
  • one -CH2 → 1 signal
  • Total = 4 signals.

Misconception: Not recognising the two terminal CH3 groups are different in 2‑iodobutane.

Q6 Which statement correctly describes 1‑iodobutane and 2‑iodobutane using ¹³C NMR?

A. 1‑iodobutane has 3 signals; 2‑iodobutane has 4

B. 1‑iodobutane has 4 signals; 2‑iodobutane has 3

C. Both have 4 signals

D. Both have 3 signals

Answer: C

Explanation: 1‑iodobutane: 4 distinct carbons → 4 signals. 2‑iodobutane: 4 distinct carbons.

Misconceptions: D assumes the two methyl groups are equivalent

Q7 Which isomer of C4H9I has the fewest ¹³C NMR signals?

A. 1‑iodobutane

B. 2‑iodobutane

C. 1‑iodo‑2‑methylpropane

D. 2‑iodo‑2‑methylpropane

Answer: D

Explanation: 2‑iodo‑2‑methylpropane ((CH3)3CI):

  • Three equivalent CH3 carbons → 1 signal
  • Central C–I carbon → 1 signal
  • Total = 2 signals (highest symmetry).

Misconception: Thinking more branching always means more signals; symmetry can reduce the number.

Q8 For 1‑iodo‑2‑methylpropane (CH3–CH(CH3)–CH2I), how many ¹³C NMR signals are expected?

A. 2     B. 3     C. 4    D. 5

Answer: B

Explanation: Carbons:

  • 2 x CH3 at one end
  • CH (attached to CH3 and CH2I)
  • CH2I All distinct → 4 signals.

Misconception: Choosing D assumes that two CH₃ groups are not equivalent; they are in different environments.

Q9 A compound with formula C4H9I shows only 2 signals in its 13C NMR spectrum. Which structure is most consistent?

A. 1‑iodobutane

B. 2‑iodobutane

C. 1‑iodo‑2‑methylpropane

D. 2‑iodo‑2‑methylpropane

Answer: D

Explanation: Only 2 distinct carbons → highly symmetric → 2‑iodo‑2‑methylpropane.

Misconception: Thinking 2 signals must mean “two carbons”; it actually means “two types of carbon”.

Q10 You have an unknown C4H9I that shows 3 distinct ¹³C signals. Which structure is most likely?

A. 1‑iodobutane

B. 2‑iodobutane

C. 1‑iodo‑2‑methylpropane

D. 2‑iodo‑2‑methylpropane

Answer: C

Explanation: 1‑iodobutane and 1‑iodo‑2‑methylpropane have 4 signals; but 1‑iodo‑2‑methylpropane gives 3 signals and highly symmetrical 2-iodo-2-methylpropane gives only 2 signals.

Misconception: Ignoring branching and symmetry when interpreting ¹³C NMR; these strongly affect the number of signals.

If you think there are any errors, please email me asap at chem55555@hotmail.com

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