1,4-diisopropylbenzene

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Gene mutation in bacteria

Read across to Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene:

- Ames test, OECD 471, S. typhimurium TA 100, TA 1535, TA 98, TA 1537 and E. coli WP2 uvrA, +/- S9, negative

 

Cytogenicity

Read across to Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene:

- Chromosome aberration test, OECD 473, Chinese hamster lung cells (CHL/IU), +/-S9, negative

 

Gene mutation in mammalian cells

Read across to 1,3-diisopropylbenzene:

- Mouse lymphoma Tk assay, OECD 476 (new OECD 490), GLP, L5178Y, +/-S9, negative

Link to relevant study records

Reference

Reference 1

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH
In this justification, the read-across (bridging) concept is applied. Please refer to a full version of Read-across statement attached in the section 13 "Assessment reports".

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
The underlying hypothesis for the read-across is that the target and the source substance have similar toxicological properties (including the same target organs) due to their structural similarity, resemblance to their chemical reactivity, and therefore a similar mode of action.
The source substance ‘Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene' is a mixture of structural isomers, 1,3- diisopropylbenzene and 1,4-diisopropylbenzene (target substance). The physico-chemical properties are highly equivalent based on the high structural similarity. As a conclusion, it is scientifically justified to address the endpoint Genetic toxicity with data on this mixture of isomers.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Source substance: Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene (Diisopropylbenzene), CAS no. 25321-09-9
structural formula: C12H18
Smiles: CC(C)C1=CC=CC=C1C(C)C
Molecular weight: 162 g/mol
CAS 25321-09-9
EC No 246-835-6
purity: not specified

target substance: 1,4-diisopropylbenzene (or p-DIPB)
structural formula: C12H18
Smiles: CC(C)c1ccc(cc1)C(C)C
Molecular weight: 162 g/mol
CAS 100-18-5
EC No 202-826-9
purity: not specified

No additional information is available on purity of the source and the target substances. Both substances are normally of high purity, containing only minor amounts of impurities that do not influence the read-across validity.

3. ANALOGUE APPROACH JUSTIFICATION
Please refer to the full version of the read-across statement attached in the section 13 "Assessment reports".

4. DATA MATRIX
Please refer to the full version of the read-across statement attached in the section 13 "Assessment reports".

Reason / purpose for cross-reference:

read-across source

Species / strain:

S. typhimurium TA 1535

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 1537

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 98

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 100

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Positive controls validity:

valid

Species / strain:

E. coli WP2 uvr A

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Positive controls validity:

valid

Additional information on results:

RANGE-FINDING/SCREENING STUDIES (if applicable):
Diisopropylbenzene was tested with a ratio of about 3 in the range of 50.0 to 5000 μg/plate. As a result, in the S9 mix-free test, antimicrobial activity was observed at 5000 μg/plate for WP2 uvrA and at all doses for the other test bacteria. In the S9 mix addition test, antimicrobial properties were observed for WP2 uvrA at 500 μg/plate or more and for the other test bacteria at more than 150 μg/plate.
Therefore, the highest dose in this study was 5000 μg/plate for WP2 uvrA and 50.0 μg/plate for other test bacteria for S9 mix-free test. In the S9 mix addition test, WP2 uvrA was tested up to 625 μg/plate, and for the other test bacteria, 200 μg/plate was used.

STUDY RESULTS
- Concurrent vehicle negative and positive control data: Please refer to attached tables

Ames test:
- Signs of toxicity: Please refer to attached tables
- Individual plate counts: Please refer to attached tables
- Mean number of revertant colonies per plate and standard deviation: Please refer to attached tables

Conclusions:

The test substance - Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene - was not mutagenic in Salmonella typhimurium TA 100, TA 1535, TA 98, TA 1537 and Escherichia coli WP2 uvrA, with or without an exogenous metabolic activation system.

Executive summary:

S. typhimurium TA 1535, TA 1537, TA 98 and TA 100 as well as E. coli WP2 uvr A were tested in a pre-incubation assay with and without metabolic activation (S9) performed according to OECD Guidelines No 471.

The test concentrations of Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene were given as follows:

-S9 mix:

0, 0.195, 0.391, 0.781, 1.56, 3.13 and 6.25 µg/plate (TA 1537)

0, 0.781 - 50.0 µg/plate (TA 100, TA 1535, TA 98 [Test 1])

0, 0.391 - 12.5 µg/plate (TA 1535 [Test 2])

0, 0.781 - 25.0 µg/plate (TA 100, TA98 [Test 2])

0, 156 - 5000 µg/plate (E. coli WP2 uvrA)

+S9 mix:

0, 6.25 - 200 µg/plate (TA 100, TA 1535, TA 98, TA 1537)

0, 19.5 - 625 µg/plate (E. coli WP2 uvrA).

 

The test substance Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene was not mutagenic in Salmonella typhimurium TA 100, TA 1535, TA 98, TA 1537 and Escherichia coli WP2 uvrA, with or without an exogenous metabolic activation system.

Based on the arguments presented in the Read Across statement attached in IUCLID Section 13, it is clear that the source substance, which consists only of the target substance and its structural isomer, shows an identical toxicokinetic pattern. As such, the data presented here could be used to fulfil lthe information requirements for the target substance 1.4-diisopropylbenzene.

Reference 2

Endpoint:

in vitro cytogenicity / chromosome aberration study in mammalian cells

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH
In this justification, the read-across (bridging) concept is applied. Please refer to a full version of Read-across statement attached in the section 13 "Assessment reports".

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
The underlying hypothesis for the read-across is that the target and the source substance have similar toxicological properties (including the same target organs) due to their structural similarity, resemblance to their chemical reactivity, and therefore a similar mode of action.
The source substance ‘Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene' is a mixture of structural isomers, 1,3- diisopropylbenzene and 1,4-diisopropylbenzene (target substance). The physico-chemical properties are highly equivalent based on the high structural similarity. As a conclusion, it is scientifically justified to address the endpoint Genetic toxicity with data on this mixture of isomers.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Source substance: Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene (Diisopropylbenzene), CAS no. 25321-09-9
structural formula: C12H18
Smiles: CC(C)C1=CC=CC=C1C(C)C
Molecular weight: 162 g/mol
CAS 25321-09-9
EC No 246-835-6
purity: not specified

target substance: 1,4-diisopropylbenzene (or p-DIPB)
structural formula: C12H18
Smiles: CC(C)c1ccc(cc1)C(C)C
Molecular weight: 162 g/mol
CAS 100-18-5
EC No 202-826-9
purity: not specified

No additional information is available on purity of the source and the target substances. Both substances are normally of high purity, containing only minor amounts of impurities that do not influence the read-across validity.

3. ANALOGUE APPROACH JUSTIFICATION
Please refer to the full version of the read-across statement attached in the section 13 "Assessment reports".

4. DATA MATRIX
Please refer to the full version of the read-across statement attached in the section 13 "Assessment reports".

Reason / purpose for cross-reference:

read-across source

Species / strain:

Chinese hamster lung (CHL/IU)

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

True negative controls validity:

not examined

Positive controls validity:

valid

Additional information on results:

RANGE-FINDING/SCREENING STUDIES (if applicable):
In order to determine the treatment concentration of the test substance used in the chromosomal abnormality test, the effect of the test substance on cell proliferation was examined. The inhibitory effect of the test substance on CHL/IU cells compared to the solvent control was measured using a monocellater TM, Olympus Optical Industry Co., Ltd. As a result, the concentration of 50 % inhibition of cell proliferation in continuous treatment was 0.03 mg/mL. In addition, both in the presence and absence of S9 mix in the short-term treatment were 0.06 mg/mL. The maximum treatment concentration in each series was twice the 50 % cell growth inhibitory concentration, and the other treatment concentrations were set at the ratio of 2.

STUDY RESULTS
- Concurrent vehicle negative and positive control data

Chromosome aberration test (CA) in mammalian cells:
- Results from cytotoxicity measurements:
Short-term treatment -S9: >= 0.015 mg/mL
Short-term treatment +S9: no cytotoxicity up to 0.015 mg/mL
Continuous treatment -S9: >= 0.03 mg/mL
- Genotoxicity results (for both cell lines and lymphocytes)
o Number of cells scored for each culture and concentration, number of cells with chromosomal aberrations and type given separately for each treated and control culture, including and excluding gaps: Please refer to attached Tables

Conclusions:

The test substance - Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene - caused no chromosomal aberrations or polyploidy in Chinese hamster lung cells (CHL/IU), with or without an exogenous metabolic activation system.

Executive summary:

The test substance - Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene - was tested in an in vitro mammalian chromosome aberration test with Chinese hamster lung cells (CHL/IU) according to OECD Guideline 473.

The test concentrations were as follows:

-S9 mix (continuous treatment; 24 or 48 hrs): 0, 0.0038, 0.0075 and 0.015 mg/mL

-S9 mix (short-term treatment; 6 hrs): 0, 0.0019, 0.0038 and 0.0075 mg/mL

+S9 mix (short-term treatment; 6 hrs): 0, 0.03, 0.06 and 0.12 mg/mL.

 

The test substance caused no chromosomal aberrations or polyploidy in Chinese hamster lung cells (CHL/IU), with or without an exogenous metabolic activation system.

Based on the arguments presented in the Read Across statement attached in IUCLID Section 13, it is clear that the source substance, which consists only of the target substance and its structural isomer, shows an identical toxicokinetic pattern. As such, the data presented here could be used to fulfil lthe information requirements for the target substance 1.4-diisopropylbenzene.

Reference 3

Endpoint:

in vitro gene mutation study in mammalian cells

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH
In this justification, the read-across (bridging) concept is applied. Please refer to a full version of Read-across statement attached in the section 13 "Assessment reports".

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
The underlying hypothesis for the read-across is that the target and the source substance have similar toxicological properties (including the same target organs) due to their structural similarity, resemblance to their chemical reactivity, and therefore a similar mode of action.
The source substance '1,3-diisopropylbenzene' is a structural isomer of 1,4-diisopropylbenzene (target substance). The physico-chemical properties are highly equivalent based on the high structural similarity. As a conclusion, it is scientifically justified to address the endpoint Genetic toxicity with data on this isomer.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Source substance: 1,3-diisopropylbenzene (m- Diisopropylbenzene; m-DIPB), CAS no. 99-62-7
structural formula: C12H18
Smiles: CC(C)c1cccc(c1)C(C)C
Molecular weight: 162 g/mol
CAS 99-62-7
EC No 202-773-1
purity: not specified

target substance: 1,4-diisopropylbenzene (or p-DIPB)
structural formula: C12H18
Smiles: CC(C)c1ccc(cc1)C(C)C
Molecular weight: 162 g/mol
CAS 100-18-5
EC No 202-826-9
purity: not specified

No additional information is available on purity of the source and the target substances. Both substances are normally of high purity, containing only minor amounts of impurities that do not influence the read-across validity.

3. ANALOGUE APPROACH JUSTIFICATION
Please refer to the full version of the read-across statement attached in the section 13 "Assessment reports".

4. DATA MATRIX
Please refer to the full version of the read-across statement attached in the section 13 "Assessment reports".

Reason / purpose for cross-reference:

read-across source

Species / strain:

mouse lymphoma L5178Y cells

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

above 2.4 mM

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

True negative controls validity:

not examined

Positive controls validity:

valid

Additional information on results:

RANGE-FINDING/SCREENING STUDIES (if applicable):
please refer to attached tables

STUDY RESULTS
- Concurrent vehicle negative and positive control data: please refer to attached tables

Gene mutation tests in mammalian cells:
- Results from cytotoxicity measurements: please refer to attached tables

- Genotoxicity results: please refer to attached tables

Conclusions:

Test item m-Diisopropylbenzene (m-DIPB) is considered to be non-mutagenic in the in vitro mammalian cell gene mutation assay (thymidine kinase locus) in mouse lymphoma L5178Y cells.

Executive summary:

 

The genetic toxicity test - an in vitro mammalian cell gene mutation assay (thymidine kinase locus) in mouse lymphoma L5178Y cells - was performed originally according to OECD guideline 476 (the test method used fully corresponds to the new OECD Guideline 490, which was issued in 2015), EU method B.17 and EPA OPPTS 870.5300 with GLP compliance. 

The test item m-Diisopropylbenzene (m-DIPB) - a structural analogue of p-DIPB) was assessed for its potential to induce mutations at the mouse lymphoma thymidine kinase locus using the cell line L5178Y.

The selection of the concentrations used in the main experiments was based on data from a pre-experiments.

In experiment I 3.00 mM (with metabolic activation) and 0.50 mM (without metabolic activation) were selected as the highest concentrations.

In experiment II 0.40 mM (with metabolic activation) and 0.20 mM (without metabolic activation) were selected as the highest concentrations.

Experiment I with and without metabolic activation and experiment II without metabolic activation were performed as a 4h short-term exposure assay.

Experiment II without metabolic activation was performed as a 24 h long-term exposure assay.

The test item was investigated at the following concentrations:

Experiment I

with metabolic activation: 0.10, 0.20, 0.40, 0.80, 1.20, 1.60, 2.00, 2.40, 2.80 and 3.00 mM and

without metabolic activation: 0.05, 0.08, 0.10, 0.15, 0.20, 0.30, 0.40 and 0.50 mM

Experiment II

with metabolic activation: 0.01, 0.02, 0.05, 0.1 0, 0.20, 0.30, 0.35 and 0.40 mM and

without metabolic activation: 0.002, 0.005, 0.01, 0.02, 0.05, 0.10, 0.15 and 0.20 mM

Precipitation of the test item was noted in the pre-experiment I with and without metabolic activation at a concentration of 2.4 mM and higher. In the experiments I and II with and without metabolic activation and in the pre-experiment II without metabolic activation no precipitation was noted.

Growth inhibition was observed in experiment I and II with and without metabolic activation.

In experiment I with metabolic activation the relative total growth (RTG) was 12.3 % for the highest concentration (3.00 mM) evaluated. The highest concentration evaluated without metabolic activation was 0.50 mM with a RTG of 21.5 %. In experiment II with metabolic activation the relative total growth (RTG) was 15.7 % for the highest concentration (0.40 mM) evaluated. The highest concentration evaluated without metabolic activation was 0.20 mM with a RTG of 7.9 %.

In experiment I and II no biologically relevant increase of mutants was found after treatment with the test item (with and without metabolic activation). The Global Evaluation Factor (GEF; defined as the mean of the negative/vehicle mutant frequency plus one standard deviation; data gathered from ten laboratories) was not exceeded by the induced mutant frequency at any concentration.

No dose-response relationship was observed.

Additionally, in experiment I and II colony sizing showed no clastogenic effects induced by the test item under the experimental conditions (with and without metabolic activation).

EMS, MMS and B[a]P were used as positive controls and showed distinct and biologically relevant effects in mutation frequency. Additionally, MMS and B[a]P significantly increased the number of small colonies, thus proving the efficiency of the test system to indicate potential clastogenic effects.

In conclusion, in the described mutagenicity test under the experimental conditions reported, the test item meta-DiisopropyIbenzene (m-DIPB) is considered to be non-mutagenic in the in vitro mammalian cell gene mutation assay (thymidine kinase locus) in mouse lymphoma L5178Y cells.

Based on the arguments presented in the Read Across statement attached in IUCLID Section 13, it is clear that the source substance, 1.3-diisopropylbenzene, which is the structural isomer of the target substance, shows an identical toxicokinetic pattern. As such, the data presented here could be used to fulfil lthe information requirements for the target substance 1.4-diisopropylbenzene.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Genetic toxicity in vitro - mouse lymphoma (mammalian cell gene mutation assay)

Read across to 1,3-diisopropylbenzene:

The test item m-diisopropylbenzene was assessed for its potential to induce mutations at the mouse lymphoma thymidine kinase locus using the cell line L5178Y. The selection of the concentrations used in the main experiments was based on data from a pre-experiments. The test item was investigated at the following concentrations: Experiment I with metabolic activation: 0.10, 0.20, 0.40, 0.80, 1.20, 1.60, 2.00, 2.40, 2.80 and 3.00 mM and without metabolic activation: 0.05, 0.08, 0.10, 0.15, 0.20, 0.30, 0.40 and 0.50 mM Experiment II with metabolic activation: 0.01, 0.02, 0.05, 0.1 0, 0.20, 0.30, 0.35 and 0.40 mM and without metabolic activation: 0.002, 0.005, 0.01, 0.02, 0.05, 0.10, 0.15 and 0.20 mM Precipitation of the test item was noted in the pre-experiment I with and without metabolic activation at a concentration of 2.4 mM and higher. In the experiments I and II with and without metabolic activation and in the pre-experiment II without metabolic activation no precipitation was noted. Growth inhibition was observed in experiment I and II with and without metabolic activation. In experiment I with metabolic activation the relative total growth (RTG) was 12.3 % for the highest concentration (3.00 mM) evaluated. The highest concentration evaluated without metabolic activation was 0.50 mM with a RTG of 21.5 %. In experiment II with metabolic activation the relative total growth (RTG) was 15.7 % for the highest concentration (0.40 mM) evaluated. The highest concentration evaluated without metabolic activation was 0.20 mM with a RTG of 7.9 %. In experiment I and II no biologically relevant increase of mutants was found after treatment with the test item (with and without metabolic activation). The Global Evaluation Factor (GEF; defined as the mean of the negative/vehicle mutant frequency plus one standard deviation; data gathered from ten laboratories) was not exceeded by the induced mutant frequency at any concentration. No dose-response relationship was observed. Additionally, in experiment I and II colony sizing showed no clastogenic effects induced by the test item under the experimental conditions (with and without metabolic activation). EMS, MMS and B[a]P were used as positive controls and showed distinct and biologically relevant effects in mutation frequency. Additionally, MMS and B[a]P significantly increased the number of small colonies, thus proving the efficiency of the test system to indicate potential clastogenic effects.

Based on the arguments presented in the Read Across statement attached in IUCLID Section 13, it is clear that the source substance, which is the isomer of the target substance, shows an identical toxicokinetic pattern. As such, the data presented here could be used to fulfill the information requirements for the target substance 1.4-diisopropylbenzene.

 

Genetic toxicity in vitro - mammalian chromosome aberration test

Read across to Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene:

The test substance was tested in an in vitro mammalian chromosome aberration test with Chinese hamster lung cells (CHL/IU) according to OECD Guideline No. 473.

The test concentrations were as follows:

-S9 mix (continuous treatment; 24 or 48 hrs): 0, 0.0038, 0.0075 and 0.015 mg/mL

-S9 mix (short-term treatment; 6 hrs): 0, 0.0019, 0.0038 and 0.0075 mg/mL

+S9 mix (short-term treatment; 6 hrs): 0, 0.03, 0.06 and 0.12 mg/mL.

The test substance caused no chromosomal aberrations or polyploidy in Chinese hamster lung cells (CHL/IU), with or without an exogenous metabolic activation system.

Based on the arguments presented in the Read Across statement attached in IUCLID Section 13, it is clear that the source substance, which consists only of the target substance and its structural isomer, shows an identical toxicokinetic pattern. As such, the data presented here could be used to fulfil lthe information requirements for the target substance 1.4-diisopropylbenzene.

Genetic toxicity in bacterial reverse mutation assay

Read across to Mixture of 1,3-diisopropylbenzene and 1,4-diisopropylbenzene:

S. typhimurium TA 1535, TA 1537, TA 98 and TA 100 as well as E. coli WP2 uvr A were tested in a pre-incubation assay performed according to OECD Guidelines No. 471.

The test concentrations were given as follows:

-S9 mix:

0, 0.195, 0.391, 0.781, 1.56, 3.13 and 6.25 µg/plate (TA 1537)

0, 0.781 - 50.0 µg/plate (TA 100, TA 1535, TA 98 [Test 1])

0, 0.391 - 12.5 µg/plate (TA 1535 [Test 2])

0, 0.781 - 25.0 µg/plate (TA 100, TA98 [Test 2])

0, 156 - 5000 µg/plate (E. coli WP2 uvrA)

+S9 mix:

0, 6.25 - 200 µg/plate (TA 100, TA 1535, TA 98, TA 1537)

0, 19.5 - 625 µg/plate (E. coli WP2 uvrA).

 

Cytotoxic effects were seen at the following concentrations:

-S9 mix:

TA 100: >= 12.5 µg/plate

TA 1535: >= 6.25 µg/plate

TA 98: >= 12.5 µg/plate

TA 1537: >= 6.25 µg/plate

E. coli: 5000 µg/plate

+S9 mix:

TA 100, TA 1535, TA 98 and TA 1537: >= 100 µg/plate

E. coli: 625 µg/plate.

 

The test substance was not mutagenic in Salmonella typhimurium TA 100, TA 1535, TA 98, TA 1537 and Escherichia coli WP2 uvrA, with or without an exogenous metabolic activation system.

Based on the arguments presented in the Read Across statement attached in IUCLID Section 13, it is clear that the source substance, which consists only of the target substance and its structural isomer, shows an identical toxicokinetic pattern. As such, the data presented here could be used to fulfill the information requirements for the target substance 1.4-diisopropylbenzene.

Justification for classification or non-classification

According to the criteria of Classification, Labelling and Packaging of Substances and Mixtures Regulation (EC) No 1272/2008 (CLP Regulation), a classification for 1,4-diisopropylbenzene is not warranted.